Patent Publication Number: US-2022212070-A1

Title: Golf club heads with internal undercuts

Description:
RELATED APPLICATIONS 
     This is a continuation in part of U.S. patent application Ser. No. 17/237,010, filed on Apr. 21, 2021, which claims the benefit to U.S. Provisional Patent Application No. 63/013,341, filed on Apr. 21, 2020. This also claims the benefit to U.S. Provisional Patent Application No. 63/200,726 all of which are incorporated herein by reference. 
    
    
     FIELD 
     The present disclosure relates generally to golf equipment, and more particularly, to flexure structures for improved performance characteristics of hollow body irons and methods to manufacture hollow body irons with flexure structures. 
     BACKGROUND 
     Hollow body irons, ideally, operate as a diving board, flexing rearward during impact. In club design, the degree to which a hollow body iron behaves as a diving board, or spring is constrained by peak stress values. To ensure that traditional golf clubs do not exceed maximum stress limits, the face and sole are thickened such that the club is made more rigid. The rigidity of the traditional golf clubs results in a degradation to the diving board, or spring behavior of the club head. Therefore, there is a need in the art to produce a golf club head having a construction which expands the limit of modifications to the face to improve energy transfer from the club to the ball at impact. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts a toe end perspective view of a hollow body club head according to one embodiment. 
         FIG. 2A  depicts a toe side cross-sectional view of the hollow body club head of  FIG. 1 . 
         FIG. 2B  depicts a view of a portion of the hollow body club head of  FIG. 2A . 
         FIG. 3  depicts a front view of an internal cavity of  FIG. 1 . 
         FIG. 4A  depicts a cross-sectional view of a hollow body club, similar to the hollow body club of  FIG. 1 , according to another embodiment comprising a ballast with an angled forward surface. 
         FIG. 4B  depicts a close-up view of the ballast and undercut of the hollow body club of  FIG. 4A . 
         FIG. 5  depicts a toe end perspective view of the hollow body club of  FIG. 4A  with the strikeface removed, showing the internal cavity. 
         FIG. 6A  depicts a cross-sectional view of a hollow body club, similar to the hollow body club of  FIG. 1 , according to another embodiment. 
         FIG. 6B  depicts a view of a portion of the hollow body club of  FIG. 6A . 
         FIG. 7  depicts a top cross-sectional view of the hollow body club of  FIG. 6A , highlighting the cascading region within the internal cavity. 
         FIG. 8  depicts a cross-sectional view of a prior art hollow body club, according to another embodiment. 
         FIG. 9  depicts comparative a graph of ball velocity of a 7 iron measured in mph for various undercut embodiments described in this disclosure. 
         FIG. 10  depicts a comparative graph of vertical launch angle of the 7 iron of  FIG. 9  in degrees for various undercut embodiments described in this disclosure. 
         FIG. 11  depicts a comparative graph of spin rate of the 7 iron of  FIG. 9  in rpm for various undercut embodiments described in this disclosure. 
         FIG. 12  depicts a comparative graph of vertical launch angle of a pitching wedge in degrees for various undercut embodiments described in this disclosure. 
         FIG. 13  depicts a comparative graph of spin rate of the pitching wedge of  FIG. 12  for various undercut embodiments described in this disclosure. 
         FIG. 14  depicts comparative a graph of ball speed of the pitching wedge of  FIG. 12 , measured in mph, for various undercut embodiments described in this disclosure. 
     
    
    
     For simplicity and clarity of illustration, the drawing figures illustrate the general manner of construction, and descriptions and details of well-known features and techniques may be omitted to avoid unnecessarily obscuring the invention. Additionally, elements in the drawing figures are not necessarily drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help improve understanding of embodiments of the present invention. The same reference numerals in different figures denote the same elements. 
     The terms “first,” “second,” “third,” “fourth,” and the like in the description and in the claims, if any, are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments described herein are, for example, capable of operation in sequences other than those illustrated or otherwise described herein. Furthermore, the terms “include,” and “have,” and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, device, or apparatus that comprises a list of elements is not necessarily limited to those elements, but may include other elements not expressly listed or inherent to such process, method, system, article, device, or apparatus. 
     The terms “left,” “right,” “front,” “back,” “top,” “bottom,” “over,” “under,” and the like in the description and in the claims, if any, are used for descriptive purposes and not necessarily for describing permanent relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the invention described herein are, for example, capable of operation in other orientations than those illustrated or otherwise described herein. 
     The terms “couple,” “coupled,” “couples,” “coupling,” and the like should be broadly understood and refer to connecting two or more elements or signals, electrically, mechanically and/or otherwise. 
     The term “ground plane,” as used herein, can refer to a reference plane associated with the surface on which a golf ball is placed. The ground plane can be a horizontal plane tangent to the sole at an address position. 
     The terms “loft” or “loft angle” of a hollow body golf club (hererafter “hollow body” or “hollow body iron” or “iron-type golf club head” or “golf club head”), as described herein, refers to the angle formed between the club face and the shaft, as measured by any suitable loft and lie machine. A loft plane lies tangent to the strikeface at the geometric center. A loft angle is measured between the ground plane and the loft plane. In many embodiments, the loft angle of the club head is less than approximately 50 degrees, less than approximately 49 degrees, less than approximately 48 degrees, less than approximately 47 degrees, less than approximately 46 degrees, less than approximately 45 degrees, less than approximately 44 degrees, less than approximately 43 degrees, less than approximately 42 degrees, less than approximately 41 degrees, less than approximately 40 degrees, less than approximately 39 degrees, less than approximately 38 degrees, less than approximately 37 degrees, less than approximately 36 degrees, less than approximately 35 degrees, less than approximately 34 degrees, less than approximately 33 degrees, less than approximately 32 degrees, less than approximately 31 degrees, less than approximately 30 degrees, less than approximately 29 degrees, less than approximately 28 degrees, less than approximately 27 degrees, less than approximately 26 degrees, less than approximately 25 degrees, less than approximately 24 degrees, less than approximately 23 degrees, less than approximately 22 degrees, less than approximately 21 degrees, less than approximately 20 degrees, less than approximately 19 degrees, less than approximately 18 degrees, 17, or less than approximately 16 degrees. Further, in many embodiments, the loft angle of the club head is greater than approximately 16 degrees, greater than approximately 17 degrees, greater than approximately 18 degrees, greater than approximately 19 degrees, greater than approximately 20 degrees, greater than approximately 21 degrees, greater than approximately 22 degrees, greater than approximately 23 degrees, greater than approximately 24 degrees, greater than approximately 25 degrees, greater than approximately 26 degrees greater than approximately 27 degrees, greater than approximately 28 degrees, greater than approximately 29 degrees, greater than approximately 30 degrees, greater than approximately 31 degrees, greater than approximately 32 degrees, greater than approximately 33 degrees, greater than approximately 34 degrees, greater than approximately 35 degrees, greater than approximately 36 degrees, greater than approximately 37 degrees, or greater than approximately 38 degrees. 
     DESCRIPTION 
     The present disclosure describes technologies for an improved hollow body iron-type golf club head (hererafter “hollow body” or “hollow body iron” or “iron-type golf club head” or “golf club head”) having a sole and ballast configured to relieve stress within a forward portion of the sole. In a first configuration, the golf club head comprises a ballast undercut for relieving stress. In other configurations, the ballast undercut is combined with additional stress relief features, such as a cascading sole near the face sole juncture, for further reductions to face thickness. 
     The hollow body can comprise a strikeface, a rear portion, opposite the strikeface, a heel portion, a toe portion, opposite the heel, a sole, and a top rail to define an interior cavity. The rear portion can further include a ballast extending forward from the rear portion and into the interior cavity. In many embodiments, the ballast is an internal component such that it is not visible from the exterior of the golf club. The ballast can further comprise a geometry configured to increase the interior surface area of the sole. For example, in some embodiments, the ballast can comprise a top surface, a forward surface, and a bottom surface defined as an undercut region. In such embodiments, when viewed from a toe side cross section, an undercut is formed by the bottom surface&#39;s concave geometry relative to the face. In other embodiments, a forward surface of the ballast may be angled towards the face such that the forward surface overhangs a portion of the sole. In such embodiments, an undercut is formed between the ballast forward surface and the interior surface of the sole. The undercut allows the thinner, forward portion of the sole to extend beneath the ballast. A ballast comprising a bottom undercut surface and/or an angled forward surface, as opposed to a forward surface that meets the interior surface of the sole at a right angle, (1) prevents stress from concentrating along the sole between the face and the ballast and (2) increases the portion of the sole capable of storing strain energy. Hollow body irons comprising an undercut, therefore, comprise sole and face geometries with greater range of thinning, as compared to hollow irons without an undercut. 
     The sole of the hollow body iron can be divided into two regions, the forward portion and the rear portion. The forward portion defines the thin region of the sole adjacent the strikeface, which can store strain energy. The rear portion of the sole describes the region of the sole adjacent to the to the rear portion of the of the body, which does not store strain energy. In other words, the forward portion of the sole  132  is the portion of the sole  110  that behaves as a spring. Hollow body irons having a thinner face and extended forward sole portion, as a result of the ballast undercut, store more strain energy (i.e., potential energy) than the face and forward sole portion of a club without an undercut. Consequently, the undercut improves the spring-like energy transfer between the club body and the golf ball (as compared to a golf club without an undercut). This energy transfer can be further improved in hollow body irons when the forward sole portion also comprises a cascade, in addition to the undercut. The cascading sole improves the flow of stress within the forward portion of the sole near the face sole juncture, while the undercut improves the flow of stress near the ballast. Accordingly, the application of the undercut and/or the combined application of the undercut and cascading sole can result in a golf club head, which can tolerate a 3-8% thinner face. Thus, the thinner face, which had been previously unattainable, results in an improved flight trajectory and distance. 
     I. Undercut 
     a. Undercut formed by Bottom Surface of Ballast 
       FIG. 1  of the drawings depicts a perspective view of an iron-type golf club head  100  exterior having an internal stress relieving sole  110  and ballast  114  having an undercut  102 , shown in  FIG. 2A . The golf club head  100  comprises a hollow body structure with an internal cavity  104 . The hollow body structure of golf club head  100  is further defined by a strikeface  106 , a rear portion  108  opposite the strikeface  106 , a heel portion  103 , a toe portion  105  opposite the heel portion  103 , a sole  110 , and a top rail  112  opposite the sole  110 . 
       FIG. 2A  illustrates a heel cut away view of the  FIG. 1  golf club head  100 .  FIG. 2A  shows the internal cavity  104  and stress relieving features of golf club head  100 . The rear portion  108  further comprises a ballast  114  located within the internal cavity  104 . As shown in  FIG. 2A , the ballast  114  is an integral weighting element necessary for optimal CG (center of gravity) positioning in golf club head  100 . The ballast  114  is a solid structure protruding vertically from the sole  110 , forward from the rear portion  108 , and extending along the sole  110  in a heel to toe direction. A forward portion  132  of the sole  110  is defined between the strikeface  106  and the ballast  114 . 
     Continuing to refer to  FIG. 2B , the ballast  114  comprises a top surface  116 , a forward surface  118 , and a bottom surface  120 . As illustrated, the bottom surface  120  is contoured to create a relief defining an undercut region  128  with undercut  102 . The undercut region  128  of the ballast  114  can be studied as an undercut region  128  of material that has been removed from the ballast  114  adjacent an interior surface  122  of the sole  110 . The undercut region  128  comprises undercut  102  and an undercut transition  141 . The undercut region  128  extends laterally in a heel to toe direction over a heel to toe length  124  of the ballast  114 . In the illustrated embodiment, the undercut  102  is generally centered within the golf club head  100  between the heel portion  103  and toe portion of the golf club head  100 . As shown in  FIG. 2B , the undercut  102  extends beneath the ballast  114 , such that forward portion  132  of the sole  110  is bounded between the face and the undercut  102 /bottom surface  120  of the ballast  114 . The forward portion  132  of the sole  110  is effectively lengthened, as compared to golf club head without an undercut (i.e., a forward portion defined between the strikeface and the forward surface of the ballast). Therefore, the undercut  102  not only reduces stress in the forward portion  132  of the sole, but creates a larger spring (i.e., the forward portion of the sole) for transferring energy back to the ball at impact. 
       FIG. 2B  depicts a zoomed-in view of the ballast  114  and undercut  102  shown in the  FIG. 2A  cross section. As shown in  FIG. 2B , the ballast  114  comprises top surface  116 , forward surface  118 , and bottom surface  120 . The ballast  114  protrudes vertically from an interior surface of the sole  110  along an interior surface of the rear portion  108 . The bottom surface  120  comprises a contoured geometry that extends inward, from the forward surface  118  toward the rear portion  108  to define the undercut  102 , which extends in a heel to toe direction. Continuing to refer to the  FIG. 2B  cross section, the ballast bottom surface  120  further comprises an undercut juncture  130  defined as the juncture between the ballast bottom surface  120  and the interior surface  122  of the sole  110 . The undercut juncture  130  is a rearmost point of the ballast bottom surface  120  that defines the undercut  102 . As shown, the forward portion  132  of the sole is defined between the strikeface  106  and the undercut juncture  130 , rather than the strikeface  106  and the forward surface  118  in a hollow body iron without undercut  102 . 
     Referring to  FIG. 2B , the undercut  102  is defined by four parameters: undercut depth  134 , undercut height  136 , undercut length  138 , an undercut sole thickness  123 . Further, the ballast bottom surface  120  can be curved such that the undercut  102  is defined between an undercut bottom edge  139  and an undercut top edge  137 . The undercut depth is measured as a perpendicular distance between a ballast forward plane  20  and the undercut juncture  130  (i.e., the rear most point of the undercut). The undercut height  136  is defined as the vertical distance between an undercut top edge  137  and an undercut bottom edge  139 . The undercut length is measured parallel to a ground plane between the undercut toe end  133  and the undercut heel end  135 . Finally, the undercut sole thickness  123  is measured as the perpendicular distance from the exterior surface of the sole  121  and an interior surface of the sole  121 . In a first embodiment, the undercut  102  has a depth  134  of 0.065 inch, a height  136  of 0.083 inch, a length of 1.16 inches. 
     The undercut depth  134 , between the ballast forward plane  20  and the undercut juncture  130 , has a range of 0.010 inch to 0.100 inch. For example, the undercut depth  134  can be 0.010 inch, 0.015 inch, 0.020 inch, 0.025 inch, 0.030 inch, 0.035 inch, 0.040 inch, 0.045 inch, 0.050 inch, 0.055 inch, 0.060 inch, 0.065 inch, 0.070 inch, 0.075 inch, 0.080 inch, 0.085 inch, 0.090 inch, 0.095 inch, or 0.100 inch. Alternatively, an undercut face depth  131  can be measured as the perpendicular distance between an interior surface of the strikeface  106  and the undercut juncture  130 . In some embodiments, the undercut depth from the face ranges from 0.200 inch to 0.500 inch. For example, the undercut depth from the face can be 0.200 inch, 0.220 inch, 0.240 inch, 0.260 inch, 0.280 inch, 0.300 inch, 0.320 inch, 0.340 inch, 0.360 inch, 0.380 inch, 0.400 inch, 0.420 inch, 0.440 inch, 0.460 inch, 0.480 inch, or 0.500 inch. 
     The undercut height  136 , measured between the undercut bottom edge  139  and undercut top edge  137 , can range from 0.030 inch to 0.200 inch. For example, the undercut height  136  range from 0.030 inch to 0.040 inch, 0.040 inch to 0.050 inch, 0.050 inch to 0.060 inch, 0.060 inch to 0.070 inch, 0.070 inch to 0.080 inch, 0.080 inch to 0.090 inch, 0.090 inch to 0.100 inch, 0.100 inch to 0.110 inch, 0.110 to 0.120 inch, 0.120 inch to 0.130 inch, 0.130 inch to 0.140 inch, 0.140 inch to 0.150 inch, 0.150 inch to 0.160 inch, 0.160 inch to 0.170 inch, 0.170 inch to 0.180 inch, 0.180 inch to 0.190 inch, or 0.190 inch to 0.200 inch. 
       FIG. 3  depicts a front view of golf club head  100  wherein the strikeface  106  is removed to expose the undercut length  138  extending from the undercut heel end  135  to the undercut toe end  132 . In some embodiments, the undercut length  138  ranges from 0.5 inch to 3.0 inches. In other embodiments, the undercut length ranges from 0.50 inch to 0.75 inch, 0.75 inch to 1.00 inch, 1.00 inch to 1.25 inches, 1.25 inches to 1.50 inches, 1.50 inches to 1.75 inches, 1.75 inches to 2.00 inches, 2.00 inches to 2.25 inches, 2.25 inches to 2.50 inches, 2.50 inches to 2.75 inches, or 2.75 inches to 3.00 inches.  FIG. 3  further shows the ballast length  124 , which can be measured from a ballast heel end  125  to a ballast toe end  127 . In some embodiments the ballast length  124  ranges from 1.0 inch to 3.0 inches. In other embodiments the ballast length  124  is 1.2 inches, 1.4 inches, 1.6 inches, 1.8 inches, 2.0 inches, 2.2 inches, 2.4 inches, 2.6 inches, 2.8 inches, or 3.0 inches. 
     The undercut length  138 , measured as the distance between the undercut heel and toe ends, may further define a percent of the ballast length  124 , to describe the portion of the ballast  114  comprising the undercut  102 . In embodiments of iron type golf club heads comprising an undercut  102 , the undercut  102  can increase the surface area experiencing impact loading. The percent ballast length can be calculated as the undercut length  138  divided by the ballast length  124 . In some embodiments, the undercut percent ballast length ranges from 20% to 100%. The length of the undercut can range from 10% the length of the ballast length up to the same length as the ballast length (i.e., 100%). For example, the percent ballast length is 20%, 25%, 30%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, or 95%. 
     In addition, an undercut transition height  142 , as shown in  FIG. 2B , is defined as the perpendicular distance between an interior surface  122  of the sole  110  and forward surface lower edge  140 . In some embodiments, the transition height  142  can range from 0.150 inch to 0.300 inch. The transition height can range from 0.150 inch to 0.160 inch, 0.160 inch to 0.170 inch, 0.170 inch to 0.180 inch, 0.180 inch to 0.190 inch, or 0.190 inch to 0.200 inch, 0.200 inch to 0.210 inch, 0.210 to 0.220 inch, 0.220 inch to 0.230 inch, 0.230 inch to 0.240 inch, 0.240 inch to 0.250 inch, 0.250 inch to 0.260 inch, 0.260 inch to 0.270 inch, 0.270 inch to 0.280 inch, 0.280 inch to 0.290 inch, or 0.290 inch to 0.300 inch In the first embodiment discussed above, the transition height is 0.185 inch. The undercut transition  141  having transition height  142  and a contoured profile allows the undercut  102  to smoothly transition to the ballast forward surface  118 . This smooth transition promotes an even flow of stress through the undercut  102  and the ballast  114 . 
     As discussed above, the undercut  102  and undercut region  128  can be considered as a region of ballast material that has been removed, when compared to iron-type golf club heads lacking an undercut. An undercut volume is defined by a surface  146  of the undercut region  128  and the ballast forward plane  20 . For example, in one embodiment, the surface  146  of the undercut region and the ballast forward plane  20  define an undercut volume of 0.018 cubic inches. In other embodiments, the undercut volume ranges from 0.018 cubic inches to 0.050 cubic inches. For example, the undercut volume can be 0.018 cubic inches, 0.020 cubic inches, 0.022 cubic inches, 0.024 cubic inches, 0.026 cubic inches, 0.028 cubic inches, 0.030 cubic inches, 0.032 cubic inches, 0.034 cubic inches, 0.036 cubic inches, 0.038 cubic inches, 0.040 cubic inches, 0.042 cubic inches, 0.044 cubic inches, 0.046 cubic inches, 0.048 cubic inches, or 0.050 cubic inches. The undercut volume can be used to calculate mass removed from the ballast  114  by the undercut region  128 . Mass is calculated by multiplying the undercut volume by the material density of the ballast  114 . For example, an undercut volume ranging from 0.018 cubic inches to 0.030 cubic inches. The undercut volume can be 0.018 cubic inches, 0.020 cubic inches, 0.022 cubic inches, 0.024 cubic inches, 0.026 cubic inches, 0.028 cubic inches, or 0.030 cubic inches. The amount of material removed from the ballast to form the undercut with a material density ranging from 6.0 g/cm 3  to 7.75 g/cm 3  or a range of mass from 1.75 grams to 2.40 grams. The amount of material removed from the ballast to form the undercut with a material density of 6.0 g/cm 3 , 6.5 g/cm 3 , 7.0 g/cm 3 , or 7.75 g/cm 3  or a mass of 1.75 grams, 2.0 grams, 2.20 grams, 2.32 grams or 2.40 grams from the ballast  114 . 
     The forward portion  132  of the sole  110  extending from the strikeface  106  to the ballast  114  affects the impact response of golf club head  100  with a golf ball. As shown in  FIG. 2B , the undercut juncture  130  is spaced further rearward from the strikeface  106  than the ballast forward surface  118 . The undercut juncture&#39;s additional distance from the strikeface  106 , means that the thinner, forward portion  132  of the sole  110  has been effectively lengthened (relative to an overall front-to-rear sole width) such that part of the forward sole portion extends beneath the ballast  114  (as compared to traditional golf club heads, which lack the undercut  102 ). A forward sole length can be measured as the perpendicular distance between the undercut juncture  130  and the strikeface  106 . In some embodiments, the effective increase in length ranges from 6% to 12%. For example, the undercut  102  can increase length of the forward sole portion  132  by 6% to 7%, 7% to 8%, 8% to 9%, 9% to 10%, and 11% to 12%. Increasing the length of the thinned out forward portion  132  of the sole  110  reduces peak stress values in golf club head  100 . Rather than behaving as a rigid connection, the undercut  102  generates stress relief at the face-sole transition by allowing the forward portion  132  of the sole  110 , between the strikeface  106  and the ballast  114 , to deflect to a greater extent under impact loads. The undercut&#39;s effective increase in forward sole  132  length increases the total surface area over which impact load is distributed for a stress reduction of 1000 psi to 2000 psi within the forward portion  132  of the sole. Undercut  102  dually reduces stress concentrations within forward sole portion  132  and increases the bending/spring effect of the forward sole portion  132 . Additionally, undercut  102  reduces peak stress values within the strikeface  106  by 2000 psi to 3500 psi. For example, the undercut can reduce peak stress values in the strikeface between 2000 psi to 2100 psi, 2100 psi to 2200 psi, 2200 psi to 2300 psi, 2300 psi to 2400 psi, 2400 psi to 2500 psi, 2500 psi to 2600 psi, 2600 psi to 2700 psi, 2700 psi to 2800 psi, 2800 psi to 2900 psi, 2900 psi to 3000 psi, 3100 psi to 3200 psi, 3200 psi to 3300 psi, 3300 psi to 3400 psi, or 3400 psi to 3500 psi. 
     Alone, the above decrease in stress, within the sole  110  and strikeface  106 , can translate to an improved wear life of golf club head  100 . In other words, golf club head  100  comprising ballast  114  with undercut  102  can be hit more times and played longer than a traditional golf club head without an undercut. For example, a hollow body golf club comprising an undercut  102  can have a failure count increase of 50 hits, 100 hits, 150 hits, 200 hits, 250 hits, or 300 hits. Fatigue failure in a cyclically loaded golf club occurs over time in locations of peak stress where small cracks form in the material. Cracks, in turn, amplify stress. Therefore, golf club head  100 , with reduced peak stresses, experiences the crack growth and eventual fatigue failure at a slower rate. 
     Alternatively, the stress reduction achieved by the above ballast  114  and undercut  102  can be leveraged to improve club performance and ball speed. In some embodiments, the ballast  114  with undercut  102  can be provided in conjunction with a thinned strikeface  106 . The extent to which the strikeface of a golf club head without the undercut  102  has been constrained by peak stress levels at the face-to-sole transition. Said another way, it is not possible to improve the performance of traditional golf clubs with a thinner face because the added stress from the thinner face results in peak stresses that exceed the critical K value. Golf club head  100 , as discussed above, comprises ballast  114  with undercut  102  for stress reduction. Therefore, in some embodiments, strikeface  106  can be thinned without raising peak stress values beyond the critical K value at the sole-to-face transition. 
     The thinness reductions can be applied throughout the face. For example, in the geometric center of the face of the undercut club, the thickness at this region of the face can range between 0.080 to 0.150 inches. The thickness of the face at the geometric center of said face can be 0.150 inches, 0.140 inches, 0.130 inches, 0.120 inches, 0.110 inches, 0.100 inches, 0.090 inches, or 0.080 inches. In the perimeter toe region of the face of the undercut iron club, the thickness of the face can range from 0.050 to 0.090 inches. The thickness of the face at the perimeter toe region can be 0.050 inches, 0.060 inches, 0.065 inches, 0.070 inches, 0.071 inches, 0.074 inches, 0.076 inches, 0.077 inches, 0.079 inches, 0.080 inches, 0.082 inches, 0.084 inches, 0.086 inches, 0,088 inches, or 0.090 inches. The thickness of the face at the heel perimeter end of the undercut iron club can range from 0.045 inches to 0.090 inches. The thickness of the face at the heel perimeter end can be 0.045 inches, 0.050 inches, 0.055 inches, 0.060 inches, 0.065 inches, 0.070 inches, 0.075 inches, 0.080 inches, 0.085 inches, or 0.090 inches. 
     In some examples, the ballast  114  with undercut  102  reduces face thickness by 0.003 inches. In other examples the undercut  102  can allow the strikeface  106  to be thinned by 0.004 inches, 0.005 inches, 0.006 inches, 0.007 inches, 0.007 inches, 0.008 inches, 0.009 inches, or 0.010 inches. In an already thin strikeface  106 , this reduction equates to a thinning of roughly 6%, or an increase in ball speed of 0.5 mph to 0.7 mph. In some examples, the undercut  102  allows the strikeface to be 3 to 8% thinner than the strikeface of a golf club head without an undercut. For example, the strikeface  106  can be 3% thinner, 4% thinner, 5% thinner, 6% thinner, 7% thinner, or 8% thinner. 
     As discussed above, the undercut region  128  has a volume representative of mass removed from ballast  114 . Ballast  114  functions as a mass pad for controlling the center of gravity (CG) for golf club head  100 , such that the undercut  102  can alter club head CG. The CG can be defined relative to a geometric center  126  of the strikeface  106 . The geometric center  126  of the strikeface  106  can be determined in accordance with Section 6.1 of the USGA&#39;s Procedure for Measuring the Flexibility of a Golf Clubhead (USGA-TPX3004, Rev. 1.0.0, May 1, 2008) (available at http://www.usga.org/equipment/testing/protocol s/Procedure-For-Measuring-The-Flexibility-Of-A-Golf-Club-Head/) (the “Flexibility Procedure”). A CG height can be defined as a vertical distance between the CG and the ground plane. A front-rear CG depth  144  can be defined as a horizontal distance between the geometric center  126  the CG. For example, the front-rear CG depth  144  can range from 0.080 to 0.110 inches. The front-rear CG depth can be 0.080 inches, 0.082 inches, 0.084 inches, 0.086 inches, 0.088 inches, 0.090 inches, 0.092 inches, 0.094 inches, 0.096 inches, 0.098 inches, 0.100 inches, 0.105 inches, or 0.110 inches. 
     A ratio of undercut face depth  131  to the front-rear CG position is constrained between 3.0 and 5.5. For example, the face depth ratio 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, or 5.0. In this range, the undercut  102  improves peak stress within the forward sole portion  132  without removing material from the ballast to the extent that CG position is compromised. 
     Furthermore, because of the CG position, the undercut does not affect the overall MOI of the club. For the purpose of determining club head moments of inertia, a coordinate system may be defined at the CG via mutually orthogonal axes (i.e., an x-axis, a y-axis, and a z-axis) (Figure not shown). The y-axis extends through the head CG from the top rail  112  to the sole  110 , perpendicular to a ground plane when the golf club head  100  is at an address position. The x-axis extends through the head CG from the heel portion  103  to the toe portion  105  and perpendicular to the y-axis. The z-axis extends through the head CG from the strikeface  106  to the rear portion  108 , and perpendicular to the x-axis and the y-axis. 
     Moments of inertia then exist about the x-axis Ixx (i e top rail-to-sole moment of inertia), about the y-axis Iyy (i.e. heel-to-toe moment of inertia) and about the z-axis (i.e. strikeface to rear). In many embodiments, the golf club head with undercut comprises a top rail-to-sole moment of inertia, Ixx, from 95 g·in 2  to 130 g·in 2 . In many embodiments, the golf club head with undercut comprises a top rail-to-sole moment of inertia Ixx greater than approximately 95 g·in 2 , greater than approximately 98 g·in 2 , greater than approximately 100 g·in, greater than approximately 102 g·in 2 , greater than approximately 103 g·in 2 , greater than approximately 104 g·in 2 , greater than approximately 105 g·in 2 , greater than approximately 106 g·in 2 , greater than approximately 110 g·in 2 , greater than approximately 115 g·in 2 , greater than approximately 120 g·in 2 , greater than approximately 125 g·in 2 , greater than approximately 130 g·in 2 , greater than approximately 135 g·in 2 , greater than approximately 140 g·in 2 , greater than approximately 6750 g·in 2 , or greater than approximately 145 g·in 2 . Further, in many embodiments, the golf club head with undercut comprises a heel-to-toe moment of inertia Iyy, which may be greater than approximately 350 g·in 2 , greater than approximately 360 g·in 2 , greater than approximately 370 g·in 2 , greater than approximately 380 g·in 2 , greater than approximately 390 g·in 2 , greater than approximately 400 g·in 2 , greater than approximately 410 g·in 2 , greater than approximately 420 g·in 2 , or greater than approximately 430 g·in 2 . In many embodiments, the golf club head with undercut comprises a heel-to-toe moment of inertia Iyy from 350 g·in 2  to 420 g·in 2 . Further, the golf club head with undercut comprises a strikeface to rear moment of inertia Izz, which may be greater than approximately 400 g·in 2 , greater than approximately 4100 g·in 2 , greater than approximately 420 g·in 2 , greater than approximately 430 g·in 2 , greater than approximately 440 g·in 2 , greater than approximately 450 g·in 2 , greater than approximately 460 g·in 2 , greater than approximately 470 g·in 2 , or greater than approximately 480 g·in 2 . In many embodiments, the golf club head with undercut comprises a strikeface to rear moment of inertia Izz from 400 g·in 2  to 450 g·in 2 . The undercut of the golf club head does not significantly alter the moment of inertia of the Ixx, Iyy, and Izz axes over a golf club head without the undercut. 
     b. Undercut formed by Angled Forward Surface of Ballast 
       FIG. 4A  illustrates a heel cut away view of an iron-type golf club head  300  comprising an alternative ballast  314  design forming an undercut  302 . The golf club head  300  is substantially similar to golf club head  100 , but for the difference in the geometry of the ballast  314  and the undercut  302 . The ballast  314  is a solid structure located within the internal cavity  304  protruding vertically from the sole  310 , forward from the rear portion  308 , and extending along the sole  310  in a heel to toe direction. A forward portion  332  of the sole  310  is defined between the strikeface  306  and the ballast  314 . The ballast  314  extends forward from the rear portion  308  towards the strikeface  306  and positions mass low and forward in the internal cavity  304 . 
     As illustrated in  FIG. 4A , the ballast  314  comprises a top surface  316 , a forward surface  318 , and a ballast juncture  317  forming a transition between the top surface  316  and the forward surface  318 . The ballast  314  does not form a bottom surface. The ballast forward surface  318  transitions directly into the sole  310 . As illustrated in  FIG. 4B , an undercut juncture  330  is formed at the transition between the forward surface  318  and the sole  310 . 
     Referring to  FIGS. 4A and 4B , the ballast forward surface  318  is angled with respect to the forward portion  332  of the sole  310 . The ballast  314  forms an acute angle  399  between the ballast forward surface  318  and the interior surface  322  of the sole  310 . The ballast angle  399  creates a configuration in which the ballast juncture  317  is located forward of the undercut juncture  330  and at least a portion of the ballast  314  extends forward relative to the undercut juncture  330  to overhang the forward sole portion  332 . Specifically, the ballast forward surface  318  overhangs at least a portion of the forward sole portion  332 . The angled configuration of the ballast  314  distributes mass low in the golf club head  300  without compromising the length of the forward sole portion  332 . In this way, the club head CG height can be lowered without a reduction in spring energy stored within the forward sole portion  332 . 
     In many embodiments, the ballast angle  399  between the ballast forward surface  318  and interior surface  322  of the sole  310  can be between approximately 30 degrees and approximately 80 degrees. In some embodiments, the ballast angle  399  can be between 30 and 50 degrees, 35 and 55 degrees, 40 and 60 degrees, 45 and 65 degrees, 50 and 70 degrees, 55 and 75 degrees, or 60 and 80 degrees. In some embodiments, the ballast angle  399  can be less than 80 degrees, less than 75 degrees, less than 70 degrees, less than 65 degrees, less than 60 degrees, less than 55 degrees, less than 50 degrees, less than 45 degrees, less than 40 degrees, less than 35 degrees, or less than 30 degrees. 
     The ballast angle  399  can be selected to allow ballast  314  to project substantially forward toward the strikeface  306 . The smaller the ballast angle  314 , the greater the ability of the ballast  314  to position mass low and forward, which provides a more desirable CG location. 
     Referring to  FIG. 4B , the angled ballast  314  defines an undercut  302  extending beneath the ballast  314 . The undercut  302  is formed between the ballast forward surface  318  and the interior surface  322  of the sole  310 . The undercut  302  can be defined as the volume of the internal cavity  304  that is both beneath the ballast forward surface  318  and above the forward portion  332  of the sole  310 . In the illustrated embodiment, the ballast forward surface  318  forms a top edge  337  of the undercut  302 , and the sole interior surface  322  forms a bottom edge  339  of the undercut  302 . The undercut  302  can further be defined as the volume bounded between the undercut top edge  337  and the undercut bottom edge  339  over a heel to toe length  324  of the ballast  314 . In the illustrated embodiment, referring to  FIG. 4B , an opening between the undercut  302  and the remainder of the internal cavity  304  is formed along a ballast forward plane  350 , wherein the ballast forward plane  350  is tangent to the ballast juncture  317  and extends parallel to the strikeface  306 . The ballast forward plane  350  defines a forwardmost boundary of the undercut  302 , and the undercut juncture  330  forms a rearmost point of the undercut  302 . 
     Similar to undercut  102 , the undercut  302  formed by the angled ballast  314  effectively lengthens the forward portion  332  of the sole  310 . The undercut  302  not only reduces stress in the forward sole portion  332 , but also creates a larger spring by lengthening the amount of thin sole  310  material that is configured to flex. This larger spring increases the amount of energy transferred back to the ball at impact. 
     Referring to  FIG. 4B , the undercut  302  comprises an undercut depth  334 , an undercut height  336 , and an undercut length (not shown). The undercut depth is measured as a perpendicular distance between a ballast forward plane  350  and the undercut juncture  330  (i.e., the rear most point of the undercut). The undercut height  336  is defined as the vertical distance between an undercut top edge  337  and an undercut bottom edge  339 . The undercut length (not shown) is measured parallel to a ground plane between the undercut toe end  133  and the undercut heel end  135 . Finally, the undercut sole thickness is measured as the perpendicular distance from the exterior surface of the sole  321  and the sole interior surface  332 . 
     In many embodiments, the undercut depth  334  between the ballast forward plane  350  and the undercut juncture  330 , can range between 0.010 inch and 0.300 inch. In some embodiments, the undercut depth  134  can range from 0.010 inch to 0.030 inch, 0.030 inch to 0.050 inch, 0.050 inch to 0.070 inch, 0.070 inch to 0.090 inch, 0.090 inch to 0.110 inch, 0.110 inch to 0.130 inch, 0.130 inch to 0.150 inch, 0.150 inch to 0.170 inch, 0.170 inch to 0.190 inch, 0.190 inch to 0.210 inch, 0.210 inch to 0.230 inch, 0.230 inch to 0.250 inch, 0.250 inch to 0.270 inch, 0.270 inch to 0.290 inch, or 0.290 inch to 0.300 inch. In some embodiments, the undercut depth  134  can be greater than approximately 0.010 inch, greater than approximately 0.015 inch, greater than approximately 0.020 inch, greater than approximately 0.025 inch greater than approximately 0.05 inch, greater than approximately 0.075 inch, greater than approximately 0.100 inch, greater than approximately 0.125 inch, greater than approximately 0.150 inch, greater than approximately 0.175 inch, greater than approximately 0.200 inch, greater than approximately 0.225 inch, greater than approximately 0.250 inch, greater than approximately 0.275 inch, or greater than approximately 0.300 inch. 
     In many embodiments, the undercut height  336 , measured between the undercut bottom edge  339  and undercut top edge  337 , can range from approximately 0.030 inch to approximately 0.500 inch. In some embodiments, the undercut height  336  can range from 0.030 inch to 0.050 inch, 0.050 inch to 0.070 inch, 0.070 inch to 0.090 inch, 0.090 inch to 0.110 inch, 0.110 to 0.130 inch, 0.130 inch to 0.150 inch, 0.150 inch to 0.170 inch, 0.170 inch to 0.190 inch, 0.190 inch to 0.210 inch, 0.210 to 0.230 inch, 0.230 inch to 0.250 inch, 0.250 inch to 0.270 inch, 0.270 inch to 0.290 inch, 0.290 inch to 0.310 inch, 0.310 to 0.330 inch, 0.330 inch to 0.350 inch, 0.350 inch to 0.370 inch, 0.370 inch to 0.390 inch, 0.390 inch to 0.410 inch, 0.410 inch to 0.430 inch, 0.430 inch to 0.450 inch, 0.450 inch to 0.470 inch, or between 0.470 inch and 0.500 inch. In some embodiments, the undercut height  336  can be greater than approximately 0.010 inch, greater than approximately 0.015 inch, greater than approximately 0.020 inch, greater than approximately 0.025 inch, greater than approximately 0.05 inch, greater than approximately 0.075 inch, greater than approximately 0.100 inch, greater than approximately 0.125 inch, greater than approximately 0.150 inch, greater than approximately 0.175 inch, greater than approximately 0.200 inch, greater than approximately 0.225 inch, greater than approximately 0.250 inch, greater than approximately 0.275 inch, greater than approximately 0.300 inch, greater than approximately 0.325 inch, greater than approximately 0.350 inch, greater than approximately 0.375 inch, greater than approximately 0.400 inch, greater than approximately 0.425 inch, greater than approximately 0.450 inch, greater than approximately 0.475 inch, or greater than approximately 0.500 inch. 
     Due to the angled nature of the ballast  314 , the undercut height  336  can vary in a front to rear direction. The ballast juncture  317 , which forms the forwardmost extent of the undercut top edge  337 , is also the highest point of the undercut top edge  337 . Accordingly, in many embodiments, the undercut height  336  decreases in a front to rear direction, with the undercut height  336  being greatest at the ballast forward plane  350  and smallest at the undercut juncture  330 . 
     In many embodiments, the undercut  302  comprises an undercut length (not shown) similar to the length  138  of undercut  102 . The undercut length is measured between the undercut heel end  335  and the undercut toe end  337 . In many embodiments, the length of undercut  302  can range from 0.5 inch to 3.0 inches. In some embodiments, the length of undercut  302  can range from 0.50 inch to 0.75 inch, 0.75 inch to 1.00 inch, 1.00 inch to 1.25 inches, 1.25 inches to 1.50 inches, 1.50 inches to 1.75 inches, 1.75 inches to 2.00 inches, 2.00 inches to 2.25 inches, 2.25 inches to 2.50 inches, 2.50 inches to 2.75 inches, or 2.75 inches to 3.00 inches. In some embodiments, the length of undercut  302  can be greater than 0.5 inch, greater than 0.75 inch, greater than 1.0 inch, greater than 1.25 inches, greater than 1.50 inches, greater than 1.75 inches, greater than 2.0 inches, greater than 2.25 inches, greater than 2.50 inches, greater than 2.75 inches, or greater than 3.0 inches. 
     In some embodiments, referring to  FIG. 5 , the ballast forward surface  318  can define a curvature in a heel to toe direction. In many embodiments, such as the embodiment illustrated in  FIG. 5 , the ballast forward surface  318  comprises a concave curvature relative to the strikeface  306 . In such embodiments, the ballast forward surface  318  is closer to the strikeface  306  near the heel portion  303  and the toe portion  305  than near the center of the golf club head  300 . The concave configuration of the ballast forward surface  318  effectively lengthens the forward sole portion  332  near the center of the golf club head in comparison to forward sole portion  332  near the heel portion  303  and the toe portion  305 . Because iron-type golf club heads typically experience peak stresses in the center of the club head and lower stresses near the heel and toe, the forward sole portion  332  can be shortened near the heel portion  303  and the toe portion  305  without sacrificing durability. 
     The concave configuration of the ballast forward surface  318  allows portions of the ballast  314  near the heel portion  303  and the toe portion  305  to extend further towards the strikeface  306 . This configuration allows the overall mass of the ballast  314  to be placed lower and further forward in the internal cavity  304 . Providing the ballast forward surface  318  with a concave curvature in a heel to toe direction allows the CG of the golf club head  300  to be controlled without sacrificing the durability of the forward sole portion  332 . In many embodiments, the curvature of the ballast forward surface  318  can be configured to complement the geometry of a cascading sole region (discussed in further detail below) or any other stress relieving feature included in the forward sole portion  332 . 
     II. Undercut and Cascading Sole 
       FIG. 6A  illustrates another embodiment of a golf club head  200  comprising a ballast  214 , undercut  202 , and a cascading forward portion  232  of the sole  210 .  FIG. 6A  depicts a cross-sectional view of golf club head  200 . Golf club head  200  is substantially similar to golf club head  100  and comprises a thin forward portion  232  of sole  210  that has been effectively lengthened via the undercut  202 . Golf club head  200  is further defined by a strikeface  206 , a rear portion  208  opposite the strikeface  206 , a heel portion  203 , a toe portion  205  opposite the heel portion  203 , a sole  210 , and a top rail  212  opposite the sole  210 . Together, these components define a hollow body club with an interior cavity  204 . The rear portion  208  further comprises a ballast  214  located within the internal cavity  204 . As shown in  FIG. 6A , the ballast  214  comprises the top surface  216 , the forward surface  218 , and the bottom surface  220 . Ballast bottom surface  220  is similar to ballast bottom surface  120 . The contoured bottom surface  220  is indented toward the rear portion  208  to create undercut  202 . 
       FIG. 6B  provides a zoomed in view of the ballast  214  and sole  210  illustrated in  FIG. 6A . As shown, the forward portion  232  of the sole  210  extends from the undercut  202  in ballast  214  to the strikeface  206 . The forward portion  232  of the sole further comprises an inner region  260  and a cascading region  262 . The cascading region  262  can comprise an internal radius transition  264  between an internal surface of the strikeface  206  and an internal surface of the sole  210 . The cascading region  262  can comprise at least two thickness tiers, or levels. The tiered structure creates successive thinning of the forward sole portion  132 . In some embodiments, the cascading region  262  can comprise an internal radius transition  264  having 2, 3, 4, 5, 6, or 7 tiers. 
     Continuing to refer to  FIG. 6B , the cascading region  262  comprises a first tier  266 , second tier  268 , and a tier transition  270  between the first tier  266  and second tier  268 . The cascading region  262  of the forward sole portion  232  can have a thickness measured as the perpendicular distance between the exterior surface  221  of the sole and interior surface  222  of the sole. This thickness can decrease in a front to rear direction over the cascading region  262 . The first tier  266  can have a first thickness  272  defined as the perpendicular distance between the exterior surface  221  and interior surface  222  of the sole within the first tier  266 . The second tier  268  can have a second thickness  274  defined within the second tier  268  as the perpendicular distance between the exterior surface  221  and interior surface  222  of the sole. In some embodiments, the first thickness  272  is greater than the second thickness  274 , such that the overall thickness of the cascading region  262  decreases in the front to rear direction. The first thickness  272  and/or the second thickness  274  can have a constant thickness over a tier length in the front to rear direction. In other embodiments, the first thickness  272  and/or the second thickness  274  can be sloped to decrease in thickness over the tier length in the front to rear direction. 
     The cascading region can comprise a first tier  266 , second tier  268 , a third tier (not shown), and a first tier transition  270  between the first tier  266  and second tier  268 , and a second tier transition between the second tier and the third tier. As described above, the cascading region of the forward sole region with three tiers can have a thickness measured as the perpendicular distance between the exterior surface of the sole and interior surface of the sole. Again, the thickness decreases in a front to rear direction over the cascading region. As described above, the first tier can have a first thickness. The second tier can have a second thickness. The third tier can have a third thickness, wherein the third tier thickness (like the first and second tier thicknesses) is measured as the perpendicular distance between the exterior surface and interior surface of the sole. In some embodiments, the first thickness is greater than the second thickness, and in turn, the second thickness is greater than the third thickness, such that the overall thickness of the cascading region  262  decreases in the front to rear direction. The first thickness and/or the second thickness and/or third thickness can have a constant thickness over a tier length in the front to rear direction. In other embodiments, the first thickness and/or the second thickness and/or third thickness can be sloped to decrease in thickness over the tier length in the front to rear direction. 
     The tier transition  270 , between a rear edge of the first tier and a forward edge of the second tier, can be declined in a front to rear direction to steadily decrease the cascading region thickness between the first thickness  272  and second thickness  274 . Alternatively, in a cascading region with two tier transitions (i.e., a first transition between the first tier and second tier, and a second transition between the second tier and third tier), the transitions can be declined in a front to rear direct to steadily decrease the cascading region thickness between the first thickness, second thickness and third thickness (or first tier, second tier and third tier). In some embodiments, such as  FIG. 6B , the tier transition  270  is linearly declined at an angle less than 45 degrees between adjacent first  266  and second tiers  268 . In some embodiments, the tier transition  270  is linearly declined at an angle ranging between 10 degrees and less than 45 degrees. The linear decline can be gradual between 5 degrees and 10 degrees, 10 degrees and 15 degrees, 15 degrees and 20 degrees, 20 degrees and 25 degrees, 25 degrees and 30 degrees, 30 degrees and 40 degrees, or 40 degrees and 45 degrees. In other embodiments, not shown, the tier transition  270  can be a steeper, and more like a step. For example, tier transition  270  can be between 45 and 50 degrees, 50 degrees and 55 degrees, 55 degrees and 60 degrees, 60 degrees and 65 degrees, or 65 degrees and 70 degrees. 
     As mentioned above, the forward sole portion  232  further comprises inner region  260  between the cascading region  262  and ballast undercut  202 . The uniform inner region  260  also comprises an inner thickness  276  defined as the perpendicular distance between the exterior surface  221  of the sole  210  and the inner surface  222  of the sole  210 . The inner thickness  276  is less than the thickness of an adjacent tier, or final tier within the cascading region  262 . As shown in  FIG. 6B , the inner thickness  276  is less than the second thickness  274 . 
     In many embodiments, the cascading region  262  comprising at least a first tier  266  and second tier  268 , and alternatively a third tier (not numbered) can comprise a specific profile configured to efficiently relieve stress within the forward sole portion  232 .  FIG. 7  illustrates one embodiment of a profile of the cascading region  262 . The cascading region  262  can comprise a perimeter separating the cascading region  262  from the inner region  260  (which forms the remainder of the forward sole region  232 ). 
     In the illustrated embodiment of  FIG. 7 , the perimeter of the cascading region  262  comprises a cascade front edge  279 , a cascade rear edge  281 , a cascade toe edge  280 , and a cascade heel edge  282 . The cascade front edge  279  extends in a heel to toe direction and is located proximate a leading edge  215  of the strikeface  206 . The cascade rear edge  281  extends in a heel to toe direction and is spaced rearwardly from the cascade front edge  279 . The cascade toe edge  280  extends between the cascade front edge  279  and the cascade rear edge  281  near the toe portion  205 . The cascade heel edge  282  extends between the cascade front edge  279  and the cascade rear edge  281  near the heel portion  203 . 
     In many embodiments, as illustrated in  FIG. 7 , the cascade rear edge  281  can be arcuate, such that the cascade rear edge  281  comprises a curvature as it extends in the heel to toe direction. In the illustrated embodiment of  FIG. 7 , the cascade rear edge  281  bows rearward relative to the strikeface  206 . As such, the cascade rear edge  281  is spaced further from the strikeface  206  near the center of the golf club head  200  than near the heel portion  203  and the toe portion  205 . In many embodiments, the cascade front edge  279  is generally parallel to the strikeface  206 . In such embodiments, the arcuate cascade rear edge  281  is therefore also bowed rearward relative to the cascade front edge  279 . 
     In some embodiments, as illustrated in  FIG. 7 , one or more of the plurality of tiers  266 ,  268 ,  269  can substantially match the curvature of the arcuate rear edge  281 . One or more of the plurality of tiers can be bowed rearward relative to the cascade front edge  279  and/or the strikeface  206 . In some embodiments wherein the ballast forward surface  218  comprises a curvature in a heel to toe direction, the curvature of the arcuate cascade rear edge  281  may substantially match the curvature of the ballast forward surface  218 . The cascading region  262  can comprise a cascading region depth  290  and a cascading region width  292 . Referring to  FIG. 7 , the cascading region depth  290  is the distance between the cascade front edge  279  and the cascade rear edge  281 , measured perpendicular to the strikeface  206 . In many embodiments, the cascading region depth  290  can range between 0.050 inch and 0.250 inch. In some embodiments, the cascading region depth  290  can be between 0.050 inch and 0.075 inch, between 0.075 inch and 0.100 inch, between 0.100 inch and 0.125 inch, between 0.125 inch and 0.150 inch, between 0.150 inch and 0.175 inch, between 0.200 inch and 0.225 inch, or between 0.225 inch and 0.250 inch. In some embodiments, the cascading region depth  290  can be greater than 0.050 inch, greater than 0.075 inch, greater than 0.100 inch, greater than 0.125 inch, greater than 0.150 inch, greater than 0.175 inch, greater than 0.200 inch, greater than 0.225 inch, or greater than 0.250 inch. In some embodiments, the cascading region depth can be approximately 0.125 inch, 0.130 inch, 0.135 inch, 0.140 inch, 0.145 inch, 0.150 inch, 0.155 inch, 0.160 inch, 0.165 inch, 0.170 inch, or 0.175 inch. In some embodiments, the cascading region depth  290  can be substantially constant in a heel to toe direction. In many other embodiments, such as described below, the cascading region depth  290  can vary in a heel to toe direction. 
     In the illustrated embodiment of  FIG. 7 , wherein the cascading region  262  comprises a rearward bowing cascade rear edge  281 , the cascading region depth  290  is greatest proximate the center of the forward sole portion  232  and lesser near the cascade heel edge  282  and cascade toe edge  280 . In many embodiments, cascading region depth  290  at the cascade heel edge  282  and/or the toe edge  280  can be between 50% and 95% than the maximum cascading region depth  290 . In some embodiments, the cascading region depth  290  at the cascade heel edge  282  and/or the cascade toe edge  280  can be between 50% and 60%, between 60% and 70%, between 70% and 80%, between 80% and 90%, or between 90% and 95% the maximum cascading region depth  290 . In some embodiments, the cascading region depth  290  can be less than 95%, less than 90%, less than 85%, less than 80%, less than 75%, less than 70%, less than 65%, less than 60%, less than 55%, or less than 50% of the maximum cascading region depth  290 . In many embodiments, such as the illustrated embodiment of  FIG. 7 , the maximum cascading region depth  290  is located at or near the center of the forward sole portion  232 . 
     The increased cascading region depth  290  near the center of the forward sole portion  232  allows the cascading region  262  to relieve peak stresses that commonly occur near the center of golf club head  200 . Similarly, in embodiments with arcuate tiers (such as the illustrated embodiment of  FIG. 7 ), each tier bows rearward near the center of the golf club head  200 , contributing to the relief of peak stresses occurring near center. Because the stress experienced in the forward sole portion  232  is not as severe near the heel portion  203  and the toe portion  205 , the cascading region  262  can comprise a lesser depth  290  near the cascade heel edge  282  and the cascade toe edge  280  and still be able to relieve such stresses. Shortening the cascading region depth  290  near the cascade heel edge  282  and the cascade toe edge  280  allows the uniform inner region  260  to be effectively lengthened near the heel portion  203  and the toe portion  205 . Effectively lengthening the uniform inner region  260 , which has a lesser thickness than any tier within the cascading region  262 , increases the bending/spring effect of the forward sole portion  232 . 
     Referring to  FIG. 7 , the cascading region width  292  is the distance between the cascade heel edge  282  and the cascade toe edge  280 , measured in a heel to toe direction (i.e. parallel to the strikeface  206 ). In many embodiments, the cascading region width  292  can range between 0.50 inch and 2.5 inches. In some embodiments, the cascading region width  292  can be between 0.50 inch and 0.75 inch, between 0.75 inch and 1.00 inch, between 1.00 inch and 1.25 inch, between 1.25 inch and 1.50 inch, between 1.50 inch and 1.75 inch, between 2.00 inch and 2.25 inch, or between 2.25 inch and 2.50 inch. In some embodiments, the cascading region width  292  can be greater than 0.50 inch, greater than 0.75 inch, greater than 1.00 inch, greater than 1.25 inch, greater than 1.50 inch, greater than 1.75 inch, greater than 2.00 inch, greater than 2.25 inch, or greater than 2.50 inch. In some embodiments, the cascading region width  292  can be less than 2.50 inches, less than 2.25 inches, less than 2.00 inches, less than 1.75 inches, less than 1.50 inches, less than 1.25 inches, or less than 1.00 inches. In some embodiments, the cascading region width  292  can be approximately 1.25 inches, 1.30 inches, 1.35 inches, 1.40 inches, 1.45 inches, 1.50 inches, 1.55 inches, 1.60 inches, 1.65 inches, 1.70 inches, or 1.75 inches. In some embodiments, the cascading region width  292  can be substantially constant in a front to rear direction. In many other embodiments, such as described below, the cascading region width  292  can vary in a front to rear direction. 
     In some embodiments, the cascade heel edge  282  and the cascade toe edge  280  can extend substantially perpendicular to the strikeface  206 , such that the cascading region width  292  is constant. In many embodiments, such as the embodiment illustrated in  FIG. 7 , cascade heel edge  282  and the cascade toe edge  280  are shaped to converge inwards such that the width  292  of the cascading region  262  is tapered in a front to rear direction. In such embodiments, the cascading region width  292  is greatest proximate the cascade front edge  279  and lesser near the cascade rear edge  291 . 
     Similar to the variable cascading region depth  290 , the tapering of the cascading region width  292  allows the uniform inner region  260  to be effectively lengthened near the heel portion  203  and the toe portion  205 . The increased cascading region width  292  near the cascade front edge  279  allows the cascading region  262  to relieve peak stresses that commonly occur at the forwardmost portions of the forward sole portion  232 . Because the stress experienced in the forward sole portion  232  is not as severe rearward of the strikeface  206 , the cascading region  262  can comprise a lesser width  292  near the cascade rear edge  281  without sacrificing durability. The tapering of the cascading region width  292  in a front to rear direction effectively lengthens the uniform inner region  260  and increases the bending/spring effect of the forward sole portion  232 . 
     Continuing to refer to  FIG. 6B , the inner region  260  of forward sole portion  232  can be effectively lengthened by ballast  214  comprising undercut  202 . Ballast  214  is substantially similar to the geometry of ballast  114 . Ballast bottom surface defines an undercut region  228  comprising the undercut  202 , undercut transition  241 , and undercut juncture  230 . As shown in  FIG. 6B , the inner region  260  is positioned adjacent undercut  202 . The undercut region  228  functions in a substantially similar manner as undercut  202  and undercut region  228 . Specifically, undercut region  228  also reduces stress concentrations within forward sole portion  232  and increases the bending/spring effect of the forward sole portion  232 . The cascading region  262  can be combined with any undercut or ballast geometry described above, including an undercut  102  formed by the bottom surface  120  of a ballast  114  or an undercut  302  formed by an angled forward surface  318  of a ballast  314 . 
     In many embodiments, performance improvements from the cascading region  262  and the undercut  202  are compounding. In other words, golf club heads having both a cascading region and undercut  202 , such as hollow body club head  200 , have a greater reduction in peak stress than golf club heads comprising one of a cascading region or an undercut. Reduction of peak stress within forward sole portion  232  increases the region&#39;s tolerance to modifications for improving ball speeds. Specifically, hollow body club  200  comprising forward sole region  232 , which is defined by undercut  202  and comprising cascading region, can comprise a thinner face (as compared to a hollow body club lacking either or both of the undercut and cascading sole). This results in better ball speeds and flight distance. In some embodiments, the undercut  202  and cascading sole  242  allow the forward portion of the sole  232  to be made more reactive. Rather than remaining rigid, the forward portion  232  can be thinned, such that the forward portion  232  behaves as a spring under impact loads. This means that the golf club head  200  is more efficient at transferring swing energy to the golf ball. The ultimate increase in ball speed via reduction in average thickness of the forward portion  232  of the sole is the result of stress reduction at the face-to-sole transition  226 . The undercut and the cascading sole work together to improve the flow of stress within the forward portion  232 , thereby reducing stress concentration levels at impact. 
     EXAMPLES 
     Example 1: Study of Undercut in Hollow Body Iron 
     As described in detail above, the ballast and undercut can be applied to a golf club head alone and in conjunction with other features, such as a cascading sole, to improve club performance. In the example below, performance improvements generated by the undercut  102  were studied by comparing a golf club head without an undercut (golf club A, hereafter “Club A”), a golf club head with an undercut (golf club B, hereafter “Club B”), a golf club head without an undercut and with a cascading sole (golf club C, hereafter “Club C”), and a golf club head with an undercut and with a cascading sole (golf club D, hereafter “Club D”). Performance improvements were measured and analyzed using finite element analysis (FEA). Specifically, FEA was used to measure peak stress values within the forward portion. Average peak stress, along with a measured surface area experiencing peak stress, were used to determine the potential for each club to efficiently transfer impact energy back to the ball. Reductions in average peak stress serve as an indicator for improved durability and potential performance enhancement via face thinning and sole thinning. 
     Each of the example Clubs A, B, C, and D were substantially similar having the same overall mass, material construction, and loft angle. Impact loading in each club was simulated at 105 mph. The example clubs each comprise unique internal cavity configurations, described above. Average peak stress between the strikeface and ballast, within the forward portion of the sole, was calculated for each example. Likewise, an area of average peak stress was calculated for each example. Finally, average peak stress within the strikeface was calculated for each example. Table 1 below, shows the peak face stress, peak stress of the forward sole portion, and the peak stress area within the forward portion of the sole, for each of the example clubs discussed below. Stress values were used to determine the undercut&#39;s effect on club performance through face and sole thinning. Example Club A was compared to Club B. Example Club C was compared to Club D. The control club head was similar to the example club heads, but devoid of any stress relieving features. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Peak Face Stress 
                 Peak Forward Sole Stress 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                   
                 Club A 
                 218469 psi 
                 158169 psi 
               
               
                   
                 Example 1 
                 217117 psi 
                 156858 psi 
               
               
                   
                 Example 2 
                 213311 psi 
                 155419 psi 
               
               
                   
                 Example 3 
                 209851 psi 
                 154689 psi 
               
               
                   
                   
               
            
           
         
       
     
     Club A 
     Club A was representative of a prior art golf club head lacking all stress relieving features and was similar to  FIG. 8 . As the representative of a traditional hollow body golf club head, Club A comprised a ballast without an undercut and without a cascading sole. Without an undercut, the forward portion of the sole and the ballast met at a substantially right angle. Likewise, without the cascading sole, the strikeface transitioned smoothly to the forward portion of the sole. 
     As shown in Table 1, FEA analysis was used to calculate a value for peak stress within the strikeface of the Club A. Under a 105 mph impact load, the peak stress of the strikeface was 218469 psi. Under the same impact load, the forward portion of the strikeface had a peak stress of 157440 psi. 
     Club B 
     Club B was representative of a hollow body golf club head with an undercut stress relieving feature. Hollow body Club B was similar to Club A, but Club B included an undercut as stress relieving feature. Rather than meeting at a right angle, the undercut allowed the forward portion of the sole to extend beneath the ballast. The undercut of Example 1 comprised a depth of 0.065 inch, a height of 0.083 inch, an undercut transition height of 0.185 inches, and 1.16 inches. 
     The values for peak face stress, peak forward sole stress, and peak stress area were determined with FEA analysis and simulated impact with a golf ball at 105 mph. The peak face stress was 217117 psi and the peak forward sole stress 156257 psi. When compared to the Club A, the undercut reduced peak stress within the strikeface by 1352 psi and reduced peak stress within the forward portion of the sole by 1183 psi. This club showed that the ballast and undercut allow the both the strikeface and forward portion of the sole to store more strain energy. This means that Club B showed improved durability and improved spring response to impact loading. 
     Club C 
     The hollow body Club C was representative of a club head comprising a forward portion of the sole with a cascade, only. Club C was similar to Club A and B, but comprised a cascading sole as a singular form of stress relief. The transition from face to sole comprised first tier, a second tier and a tier transition between the first tier and the second tier. The first tier had a first tier thickness and second tier thickness, less than the first tier thickness. The tier transition was sloped to gradually transition the first tier thickness to the second tier thickness. The example did not comprise an undercut and the forward portion of the sole and ballast met at a substantially right angle. 
     Referring again to Table 1, the Example 2 hollow body golf club head had a peak face stress of 213311 psi, or a 5158 psi reduction of peak stress within the strikeface. The Example 2 club had a peak forward sole stress of 154742 psi (pounds per square inch), or a reduction in peak forward sole stress of 2698 psi This example showed that cascading sole reduced stress through increased storage of strain energy for improved durability and spring response under impact loading. 
     Club D 
     Club D was representative of a club head comprising an undercut and a cascading sole as two forms of stress relief for the strikeface and forward sole portion. The ballast comprised an undercut, which effectively lengthened the forward sole portion beneath the ballast. The cascading sole comprised a first tier, a second tier, and a tier transition between the first and second tiers. The first tier comprised a first tier thickness and the second tier comprised a second tier thickness, less than the first tier thickness. The tier transition was sloped to gradually transition the first tier thickness to the second tier thickness. 
     Club D was also subjected to FEA analysis under simulated ball impact at 105 mph. The peak face stress was 209851 psi, for a reduction of peak stress in the strikeface of 8618 psi. In other words, the Club D had a 4% reduction in peak stress within the strikeface. The peak stress of the forward sole portion was 154689 psi. The forward sole portion had a peak stress reduction of 3480 psi, or a 2.2% reduction from the Club A. This example showed that the undercut and cascading sole worked together to reduce peak stresses. Further, this example indicated that the forward portion of the sole could tolerate additional loading without reaching fatigue failure. The example showed that ball speed could be improved by thinning the face and sole to match the loading capacity of the forward sole portion. 
     The peak stresses of the forward sole portion in each of the club heads, specifically, indicated the potential for adjusting sole and face thickness and the resulting changes to ball speed. The peak stress of the forward sole portion was compared to the critical K yield stress value of the forward sole portion. Stresses that indicated that the strikeface and sole must be thickened, signaled that the internal cavity configuration would have reduced ball speed. Stresses that indicated that the strikeface and sole could be thinned, signaled that the internal cavity configuration would have increased ball speed. 
     Club A and Club B were compared to each other relative to a critical K value of 156 ksi. The peak stress of Club A, without an undercut, was 158169 psi. This peak stress value suggested that the sole and face would have needed to be thickened by roughly 2.5% in order to achieve stress values that did not exceed 156 ksi. The thickened face and sole indicated that the internal cavity configuration that would degrade ball speed. Club B, which comprised an undercut, improved peak stress within the forward sole portion. Club B had a peak stress of 156868 psi. The lower peak stress of Club B indicated Club B required the sole and face to be thickened less than the sole and face of Club A. These results showed that, after modifications, Club B and the undercut indicated better ball speed over Club A, without an undercut. 
     Similarly, Club C and Club D were compared to each other relative to the same critical K value of 156 ksi. The peak stress of Club C, with a cascading sole and without an undercut, was 155416 psi. Club C, with peak stress slightly less than the critical K stress, indicated that no modifications for improving or degrading ball speed would have been necessary. The slightly lower peak stress did indicate that the cascading sole in Club C would have increased durability. Club D comprised an undercut in addition to the cascading sole and had a peak stress of 154689 psi. Club D showed that the undercut provided further reduction to peak stress. This reduction in stress indicated that Club D had a face and sole that could tolerate thinning in order to improve ball speed. 
     The comparison of Club A and Club B and the comparison of Club C and Club D showed that the undercut reduced peak stress within the forward portion of the sole. These results further showed that the undercut could be applied to hollow body golf club heads to improve ball speed by leveraging stress reduction to thin the face and sole. 
     Example 2: Club Performance with Undercut 
     In a second example, player testing of physical clubs was used to study the performance benefits of the undercut. In this example, a 7 iron comprising an undercut was compared to a structurally similar 7 iron, which lacked an undercut. The sole and face of the 7 iron having the undercut were optimized and reduced in thickness. Over 700 shots were taken on each golf club to analyze ball speed, launch angle, and spin rate. 
       FIG. 9  compared the average ball speed of the 7 iron having an undercut and the 7 iron without an undercut. The average ball speed of the iron with the undercut was 119.7 mph. The average ball speed of the iron without the undercut was 118.7 mph.  FIG. 10  compared the average vertical launch angle of the 7 iron with an undercut and the 7 iron without the undercut. The data showed that the 7 iron with the undercut and the 7 iron without the undercut had substantially similar launch angles.  FIG. 11  compared the average spin rate of the same 7 iron with an undercut and 7 iron without an undercut. The 7 iron without an undercut had an average spin rate of 6079.9 rpm. The 7 iron without an undercut had a reduction in average spin with 5990.6 rpm. 
     Finally, the stat area (data not shown) of the 7 iron with the undercut was compared to the 7 iron without the undercut. The stat area data was used to determine the consistency of each of the golf club heads by plotting shot distance according to the left-right deviation from a straight shot. The 7 iron without the undercut had a distance deviation of 20 m, while the 7 iron with the undercut had a distance deviation of 14 m. The data showed that the undercut 7 iron produced shots that with more consistent distance. 
     The player results of Example 2 highlighted the performance benefits of the undercut. Specifically, the data showed that the undercut reduced spin on low lofted golf club heads, such as a 7 iron, and improved ball speed for improved distance. Reduced spin on low lofted golf clubs was preferred due to the distance requirements and expectations of longer, low lofted golf clubs. The Example also highlighted a tighter stat area for irons with an undercut and showed that the undercut irons performed more consistently for distance. 
     Example 3: Club Performance with Undercut and Cascading Sole Region 
     In a third example, automated testing of physical clubs using a golf swing apparatus was used to study the increased performance of an exemplary club head comprising an undercut in conjunction with a cascading region within the forward sole portion. The ball speed the exemplary club head was compared to the ball speed of a structurally similar control club head, which lacked an undercut. The exemplary club head was similar to club head  300  described above and comprised an undercut formed by the angled forward surface of a ballast. The exemplary club head further comprised a cascading region with a profile similar to cascading region  262 , wherein the cascading region depth was greater near the center of the club head than near the heel and toe. The control club head was devoid of an undercut and comprised a ballast that met the sole at a substantially right angle. The control club head further comprised a cascading region with a rectangular profile, wherein the cascading region depth was constant in a heel to toe direction. 
     The inclusion of the angled ballast in the exemplary club head led to a reduction in CG height (measured vertically from the ground plane). The exemplary club head comprised a CG height of 0.580 inch and the control club head comprised a CG height of 0.654 inch. The control club head exhibited a reduction in CG height of 0.074 inch. 
     Table 2 below compares the average ball speed of exemplary club head in comparison to the average ball speed of the control club head. The ball speed of each club was measured both on center hits and low-center hits (i.e. strikes occurring 0.25 inches below center). 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Ball Speed (mph) 
               
            
           
           
               
               
               
               
               
            
               
                   
                 Club Head 
                 Control 
                 Exemplary 
                 Increase 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 Center Hit 
                 139.1 
                 140.1 
                 1.0 
               
               
                   
                 Low Center 
                 134.3 
                 137.8 
                 3.5 
               
               
                   
                   
               
            
           
         
       
     
     Referring to Table 2, the exemplary club head exhibited significant ball speed gains over the control club head for both center hits and low-center hits. In particular, the exemplary club head exhibited a 1.0 mph increase over the control club head on center hits and a 3.5 mph increase over the control club head on low-center hits. The angled ballast, undercut, and variable depth cascading region resulted in significant improvements in ball speed, particularly on low-center shots, which is a common mis-hit for an iron-type club head. 
     In general, lowering the CG in an iron-type club head results in an increase in ball speed. The lowering of the CG height in the exemplary club head achieved by the inclusion of the angled ballast provided a significant contribution to the increase in ball speed of the exemplary club over the control club. 
     The variable depth cascading region of the exemplary club head further contributed to the increase in ball speed over the control club head comprising a rectangular cascading region. The variable depth cascading region effectively lengthened the uniform inner region of the exemplary forward sole portion near the heel and toe. Therefore, the proportion of the forward sole portion made up by the uniform inner region was greater in the exemplary club head, and the proportion of the forward sole portion made up by the cascading region was greater in the control club. Because the uniform inner region comprises a lesser thickness than the cascading region, the forward sole portion of the exemplary club head was able to store more spring energy. The increase in spring energy of the exemplary forward sole portion is especially significant in the drastic increase in ball speed measured on low-center hits. 
     The undercut of the exemplary club head allows for a further potential increase in ball speed by effectively lengthening the forward sole portion. Effectively lengthening the forward sole portion reduces peak stress within the forward sole portion. Although the sole and strikeface thicknesses of the exemplary club head and the control club head were the same, the extra stress relief achieved by effectively lengthening the forward sole portion would allow for the sole and/or strikeface to be thinned without sacrificing the durability of the forward sole portion. Such thinning would allow the exemplary club head to store more spring energy and achieve even greater ball speeds. 
     Example 4: Wet and Dry Conditions Performance with Undercut 
     In a fourth example, player testing of physical clubs was used to study the performance benefits of the undercut in varying turf conditions. In this example, a pitching wedge comprising an undercut was compared to a structurally similar pitching wedge, which lacked an undercut. Each golf club was hit in wet conditions and dry conditions and values for average launch angle, spin rate, and ball speed were measured. 
       FIG. 12  compared the launch angle of a wedge with an undercut and a wedge without an undercut in both wet conditions and dry conditions. The wedge with an undercut had an average launch angle of 24.0 degrees in dry conditions and an average launch angle of 24.5 degrees in wet conditions. The wedge without an undercut had an average launch angle of 23.6 degrees in dry conditions and an average launch angle of 25.1 degrees in wet conditions. Therefore, launch angle in wedges with an undercut and without an undercut was comparable under wet conditions. 
       FIG. 13  compared the spin rate of the same wedge with an undercut and wedge without an undercut in both wet and dry conditions. The wedge with an undercut had an average spin rate of 8617 rpm (revolutions per minute) in dry conditions and an average spin rate of 8031 rpm in wet conditions. The wedge without an undercut had an average spin rate of 8310 rpm and a spin rate of 7144 rpm in wet conditions. Therefore, the wedge with the undercut had increased spin rates to indicate better turf interaction in both wet and dry conditions for the undercut wedge. 
       FIG. 14  compared the ball speed of the wedge with the undercut and the wedge without the undercut. The wedge with the undercut had an average ball speed of 97.3 mph (mile per hour) in dry conditions and an average ball speed of 96.9 mph in wet conditions. The wedge without the undercut had an average ball speed of 97.4 mph in dry conditions and an average ball speed of 96.9 mph in wet conditions. The ball speed for the wedge with the undercut and wedge without the undercut were comparable in both wet and dry conditions. 
     The data above showed that the pitching wedge with the undercut performed more consistently in variable turf conditions than the wedge without an undercut. The launch angle of the wedge with the undercut varied by 0.5 degrees between wet and dry conditions, while the wedge without the undercut had a launch angle that 1.5 degrees. The data showed that the launch angle of the wedge without the undercut varied three times as much as the wedge with the undercut. Similarly, the spin rate of the ball coming off the wedge with the undercut was more consistent than the spin rate of the wedge without the undercut. The spin rate varied by just 586 rpm between dry and wet conditions for the wedge with the undercut, while the spin rate varied by 1166 rpm between dry and wet conditions for the wedge without the undercut. Consistent spin rates for wet and dry conditions of the undercut wedge were preferred, as the purpose of wedge-type golf clubs is consistent ball delivery on the green regardless of weather conditions. The ball speed of the wedge with and without the undercut were substantially similar. 
     Clause 1: A golf club head comprising: a hollow body defining an enclosed internal cavity, the hollow body comprising: a strikeface; a heel portion; a toe portion opposite the heel portion; a sole; a top rail; a rear portion extending between the top rail and the sole, and separated from the strikeface by the internal cavity; a solid ballast within the internal cavity extending substantially between the heel portion and the toe portion; wherein the solid ballast extends upward from the sole and forward from the rear portion; wherein the solid ballast comprises a ballast top surface, a ballast forward surface, and a ballast juncture between the ballast top surface and the ballast forward surface; a ballast forward plane tangent to the ballast juncture and parallel to the strikeface; wherein a ballast angle is defined between the ballast forward surface and an interior surface of the sole; wherein the ballast angle is between 30 and 80 degrees; an undercut formed between the ballast forward surface and the interior surface of the sole; wherein the undercut comprises: an undercut bottom edge formed by the interior surface of the sole; an undercut top edge formed by the ballast forward surface; an undercut juncture located at a transition between the interior surface of the sole and the ballast forward surface; an undercut height measured as a vertical distance between the undercut bottom edge and the undercut top edge; and wherein the undercut height measured at the ballast forward plane is greater than 0.250 inch. 
     Clause 2: The golf club head of clause 1, further comprising: a cascading region defining an internal transition region from the strikeface to the sole, the cascading region comprising; a first tier comprising a first thickness; a second tier comprising a second thickness different than the first thickness; and a tier transition region between the first tier and the second tier. 
     Clause 3: The golf club head of clause 2, further comprising a cascading region perimeter defining a boundary between the cascading region and the sole; and wherein the cascading region perimeter comprises a cascade front edge proximate a leading edge of the strikeface and a cascade rear edge spaced rearwardly from the strikeface. 
     Clause 4: The golf club head of clause 3, wherein the cascade rear edge is arcuate and bows rearward relative to the cascade front edge; wherein the cascading region comprises a depth measured as a front-to-rear distance between the cascade front edge and the cascade rear edge; and wherein the depth of the cascading region is greater proximate a center of the club head than the depth of the cascading region near the toe portion and the heel portion. 
     Clause 5: The golf club head of clause 3, wherein a width of the cascading region is greater proximate the cascade front edge than near the cascade rear edge. 
     Clause 6: The golf club head of clause 1, further comprising an undercut depth measured as a perpendicular distance between the ballast forward plane and the undercut juncture; wherein the undercut depth is greater than 0.100 inch. 
     Clause 7: The golf club head of clause 1, wherein the ballast angle is between 60 degrees and 80 degrees. 
     Clause 8: The golf club head of clause 1, wherein the ballast forward surface comprises a concave curvature relative to the strikeface. 
     Clause 9: The golf club head of clause 1, further comprising a top rail-to-sole moment of inertia ranging from 95 g·in 2  to 130 g·in 2  and a heel-to-toe moment of inertia ranging from 350 g·in 2  to 420 g·in 2 . 
     Clause 10: A golf club head comprising: a hollow body defining an enclosed internal cavity, the hollow body comprising: a strikeface; a heel portion; a toe portion opposite the heel portion; a sole; a top rail; a rear portion extending between the top rail and the sole, and separated from the strikeface by the internal cavity; a solid ballast within the internal cavity extending substantially between the heel portion and the toe portion; wherein the solid ballast extends upward from the sole and forward from the rear portion; wherein the solid ballast comprises a ballast top surface, a ballast forward surface, and a ballast juncture between the ballast top surface and the ballast forward surface; a ballast forward plane tangent to the ballast juncture and parallel to the strikeface; wherein a ballast angle is defined between the ballast forward surface and an interior surface of the sole; wherein the ballast angle is between 30 and 80 degrees; an undercut formed between the ballast forward surface and the interior surface of the sole; wherein the undercut comprises: an undercut bottom edge formed by the interior surface of the sole; an undercut top edge formed by the ballast forward surface; an undercut juncture located at a transition between the interior surface of the sole and the ballast forward surface; a cascading region defining an internal transition region from the strikeface to the sole, the cascading region comprising; a first tier comprising a first thickness; a second tier comprising a second thickness different than the first thickness; a tier transition region between the first tier and the second tier; wherein the cascading region comprises a perimeter boundary comprising a cascade front edge proximate a leading edge of the strikeface, a cascade rear edge spaced rearwardly from the strikeface, a cascade heel edge extending between the cascade front edge and the cascade rear edge proximate the heel portion, and a cascade toe edge extending between the cascade front edge and the cascade rear edge proximate the heel portion; wherein the cascading region comprises a depth measured as a front-to-rear distance between the cascade front edge and the cascade rear edge; wherein the depth of the cascading region is greater proximate a center of the club head than the depth of the cascading region near the toe portion and the heel portion; and wherein the depth of the cascading region at the cascade heel edge is between 50% and 90% of the depth of the cascading region at the center of the club head. 
     Clause 11: The golf club head of clause 10, wherein the cascading region further comprises a cascading region depth measured between the cascade heel edge and the cascade toe edge in a heel to toe direction; wherein the cascading region depth is greater near the cascade front edge than near the cascade rear edge. 
     Clause 12: The golf club head of clause 10, wherein the cascade rear edge is arcuate and bows rearward relative to the cascade front edge. 
     Clause 13: The golf club head of clause 10, wherein the cascading region further comprises a third tier. 
     Clause 14: The golf club head of clause 10, wherein the tier transition region linearly declines at an angle less than 45 degrees. 
     Clause 15: The golf club head of clause 10, wherein the ballast forward surface comprises a concave curvature relative to the strikeface. 
     Clause 16: The golf club head of clause 10, wherein the ballast angle is between 60 degrees and 80 degrees. 
     As the rules to golf may change from time to time (e.g., new regulations may be adopted or old rules may be eliminated or modified by golf standard organizations and/or governing bodies), golf equipment related to the methods, apparatus, and/or articles of manufacture described herein may be conforming or non-conforming to the rules of golf at any particular time. Accordingly, golf equipment related to the methods, apparatus, and/or articles of manufacture described herein may be advertised, offered for sale, and/or sold as conforming or non-conforming golf equipment. The methods, apparatus, and/or articles of manufacture described herein are not limited in this regard. 
     Although a particular order of actions is described above, these actions may be performed in other temporal sequences. For example, two or more actions described above may be performed sequentially, concurrently, or simultaneously. Alternatively, two or more actions may be performed in reversed order. Further, one or more actions described above may not be performed at all. The apparatus, methods, and articles of manufacture described herein are not limited in this regard. 
     While the invention has been described in connection with various aspects, it will be understood that the invention is capable of further modifications. This application is intended to cover any variations, uses or adaptation of the invention following, in general, the principles of the invention, and including such departures from the present disclosure as come within the known and customary practice within the art to which the invention pertains.