Abstract:
The present specification discloses a new self-aligning rifle bullet. The resulting bullet offers greatly improved rifle accuracy and reduction in aerodynamic drag for better long range shooting. The resulting improvements will help shooters achieve longer ranges, higher scores, smaller group sizes, and higher probabilities of first shot hits.

Description:
CROSS REFERENCES 
       [0001]    None. 
       GOVERNMENTAL RIGHTS 
       [0002]    None. 
       BACKGROUND OF THE INVENTION 
       [0003]    The present disclosure is for a self-aligning rifle bullet offering better accuracy and aerodynamic performance. Increasing the long-range accuracy of rifle bullets is a subject well represented in the prior art. Much of the prior art is directed to adjustments in the rifle. Other prior art proposes changes to the bullet. Following is a brief discussion of accuracy problems that still remain unresolved by current or prior art solutions. 
         [0004]    The French Army adopted the first aerodynamically designed long-range rifle bullet known as the “Balle D” bullet in 1898 for an 8×50 mmR Lebel smokeless powder service cartridge. The Balle D bullet was a lighter weight, spire pointed, boat-tailed rifle bullet made of a monolithic brass alloy. It could fly faster and farther than the earlier round nosed, heavy for caliber, cupro nickel jacketed, lead cored bullets it replaced. By 1906, every major army had adopted the version of this more aerodynamic bullet. These were the first generation tangent ogive bullets, and they have been the accepted norm for best accuracy in rifle shooting at all ranges. In fact, the majority of current standard issue target rifles use a 1.5-degree throat angle originally optimized for firing these tangent ogive bullets. 
         [0005]    In the mid 1980&#39;s, ballistician William C. Davis developed a secant ogive boat-tailed Very Low Drag (VLD) bullet design. The purpose of the invention was to serve as a more efficient long-range target rifle bullet. Many of the current accurate long-range rifle bullets are characterized as this second generation jacketed and lead cored VLD bullets. However, with current VLD bullets, riflemen have discovered two major problems—each stemming from what is known as in-bore yaw. 
         [0006]    In-bore yaw occurs during firing when long nosed, short bodied, secant ogive bullets become canted at an angle to the bore of the rifle upon engraving of the bullet by the bore rifling. Once this happens, the bullet becomes off balance. Current VLD bullets are not designed to correct themselves during the remainder of their trip through the barrel and therefore the resulting trajectory of the bullet is altered. The impairment in the trajectory causes variability in target impact points. Moreover, the in-bore yaw causes the center of gravity (CG) of these VLD bullets to shift laterally off the bore axis and fly with rather large initial coning angles. These problems degrade the long-range accuracy of the bullet and result in an increased atmospheric drag and crosswind sensitivity than what is intended by the original design. 
         [0007]    In response to the in-bore yaw and static imbalance problems associated with these jacketed, lead-cored VLD bullets, many long rang target shooters have chosen to select redesigned barrels. The purpose of the redesigning the rifling of the rifle barrel is to provide the slowest possible barrel twist rates. This is done in an effort to marginally stabilize their VLD match bullets. Unfortunately, one side effect of a lower barrel twist rate is a decrease in the gyroscopic stability (Sg) of the fired bullets. This tradeoff results in instability of the fired bullets at long ranges. 
         [0008]    Recognizing the shortcomings of selecting barrels having slower twist rates, other shooters have opted to make adaptations to the bullet design. One popular design is known as the Berger Hybrid Ogive bullet design. This Berger Hybrid Ogive bullet design is a variant of a VLD design utilizing a modified head shape. The ogive-generating curve of a bullet is the calculated curvature of the nose of the bullet. In this context, the base portion of the ogive of Berger hybrid bullet is a type of tangent ogive, while the remainder of the hybrid ogive is a shortened secant ogive design ending in a rather large diameter (.15 caliber) blunt meplat. Although somewhat effective at managing the VLD accuracy problem, much of the aerodynamic advantage of using a secant ogive versus a tangent ogive nose shape has been traded away in this dual ogive design, i.e., the Berger Hybrid design only improves the VLD style bullet guidance problem at the front end of its dual ogive, while the rear portion of the bullet is still free to shift around within the necessary case neck and ball seat clearances. 
         [0009]    Current solutions do not completely satisfy the VLD accuracy problem, but instead result in a give and take—gaining accuracy in some areas while losing aerodynamic efficiency in others. The present invention provides a much better solution. The present invention reduces or eliminates in bore yaw, thereby allowing shooters to select faster barrel twist rates and achieve greater accuracy at longer ranges, while also solving the shifting problem inherent to the Berger Hybrid Ogive bullet design. 
       BRIEF SUMMARY OF THE INVENTION 
       [0010]    The present specification discloses a new type of self-aligning, ultra low drag rifle bullet that solves the shortcomings of the prior art. It offers both greatly improved rifle accuracy and an average 15 percent further reduction in aerodynamic drag for better long range shooting. 
         [0011]    This new self-aligning bullet utilizes a small meplat, a secant ogive design, a foreshank, a conical ramp, a rear-driving band, a boat tail, and a rear-bore cavity—all calculated to achieve greater accuracy. Most importantly, the resulting bullet is designed to be self-aligning in the rifle barrel. This alignment is independent of the design of the chamber and throat in the rifle firing it. These and other advantages will become apparent from the following detailed description which, when viewed in light of the accompanying drawings, disclose the embodiments of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a perspective view of the bullet 
           [0013]      FIG. 2  is a perspective view of the bullet 
           [0014]      FIG. 3  is a side view of the bullet 
           [0015]      FIG. 4  is a rear view of the bullet 
           [0016]      FIG. 5  is a front view of the bullet 
           [0017]      FIG. 6  is a longitudinal cross section of the first preferred embodiment of the bullet 
           [0018]      FIG. 7  is a longitudinal cross section of the second preferred embodiment of the bullet 
           [0019]      FIG. 8  is a detailed view of the longitudinal cross section of the second preferred embodiment of the bullet 
       
    
    
     LISTING OF COMPONENTS 
       [0000]    
       
         
           
               101 —Meplat 
               103 —Secant Ogive Nose 
               105 —Ogive Base 
               107 —Foreshank 
               109 —Conical Ramp 
               111 —Rear-Driving Band 
               113 —Boat Tail 
               115 —Base 
               117 —Rear Base Cavity 
               119 —Core Material 
               121 —Internal Relief Groove 
               123 —Tapered Ramp 
           
         
       
     
       DETAILED DESCRIPTION OF THE INVENTION 
       [0032]    The basic bullet shape in this first preferred embodiment includes a meplat  101 , a secant ogive nose  103 , an ogive base  105 , a foreshank  107 , a conical ramp  109 , a rear-driving band  111 , a boat tail  113 , a base  115 , and a rear base cavity  117 . 
         [0033]    In the first preferred embodiment, the self-aligning bullet is made from rod stock of machining brass alloy in an automated computerized numerical control (CNC) turning center in any of the various calibers currently favored for long range rifle shooting. Except for minor variations to accommodate caliber specific bore and groove diameter standards, the first preferred embodiment of the self-aligning bullet invention will have an outside profile and shape that is generally scalable by caliber size. 
         [0034]    For purposes of calculating and replicating a standard design of the self-aligning bullet invention, the bore diameter of the rifle barrel is assigned a 1.0 caliber reference diameter point. This approach differs from the usual rifle bullet design practice of using the nominal groove diameter of standard rifle barrels. For purposes of establishing relative dimensions disclosed herein the overall length of the complete bullet is understood to be approximately 5.5 calibers. 
         [0035]    Beginning with the tip of the bullet, as shown on  FIG. 1 , there is a meplat  101 . In this preferred embodiment, the meplat  101  is very small when compared to other prior are bullet designs. This small, inscribed spherical meplat  101  is tangent to the secant arc at approximately the .09-.11 caliber diameter point. 
         [0036]    The meplat  101  is the tip of the secant ogive nose  103 . In this preferred embodiment, the secant ogive nose  103  is approximately 2.9-3.1 calibers in length. The length of the secant ogive nose  103  is longer than other standard VLD bullet designs. Its approximate 18.5 caliber radius of curvature of the secant ogive-generating curve is twice the radius of curvature (9.25 calibers) of a similar 3.0 caliber tangent ogive bullet design. These dimensions, e.g., having a secant ogive with twice the generating radius of a tangent ogive for that same nose length, are understood to be almost the lowest drag nose shape possible. 
         [0037]    As part of the overall secant ogive nose  103  there is also an ogive base  105 . In this preferred embodiment, the outside diameter of the ogive base  105  is preferentially calculated using the bore diameter of the rifle barrel (rather than using the traditional method of using groove diameter). The ogive base  105  has an approximate outside diameter equal to the bore diameter of the rifle barrel (+) 0.0002 inches. Sizing the ogive base  105  in this manner creates an average of 5.5 percent reduction in cross-sectional area when compared to the prior art. 
         [0038]    Adjacent to the ogive base  105  is a foreshank  107 . The cylindrical foreshank  107  has a length of approximately 1.1-1.3 calibers and an approximate outside diameter equal to the bore diameter, plus (+) 0.0002 inches. The foreshank  107  will mechanically center the front of the bullet inside the rifling lands. As the bullet enters the rifling during firing, the foreshank  107  provides the proximal guidance to keep the bullet concentric to the bore. The foreshank  107  and conical ramp  109  represents the self-aligning region of the bullet. 
         [0039]    The conical ramp  109  has a proximal end connecting to the foreshank  107  and a distal end connected to a rear-driving band  111 . The angle between these two points preferentially forms an approximate 7.0-8.0 degree incline towards the rear-driving band  111 . This conical ramp  109  is a caliber specific width averaging approximately .10 calibers for rifle bullets and joins the proximal end of the rear-driving band approximately 1.2-1.4 calibers distal to the ogive base  105 . The design of the conical ramp  109  centers the rear of the bullet and serves two important purposes. First, the proximal end of the conical ramp  109  increases the lug contact area, thereby minimizing the shearing of the brass driving band material as spin up torque is rapidly applied to the bullet during firing. Second, the approximate 7.0-8.0 degree angle serves to center the distal end of the bullet on the barrel axis as it enters the smaller cone angled throat of a target rifle. Thus the axis of the bullet is forcefully centered on the axis of the rifle barrel at two separate places. 
         [0040]    In this first preferred embodiment, the rear-driving band  111  is located distal to the conical ramp  109  yet proximal relative to the boat tail  113 . The rear-driving band  111  is designed to be wider and larger in diameter than in other prior art designs. This allows the bullet to be firmly seated into a self-contained rifle cartridge case, confers better obturation of the brass bullet in the rifle barrel, and allows the bullet to withstand the rigors of rifle interior ballistics. The rifle caliber specific top widths of the rear-driving band  111  vary from .54 calibers to .65 calibers. The outside diameter of the rear-driving band  111  varies from 1.020 calibers to 1.034 calibers, but is always approximately equal to the standard groove diameter, (+) 0.0002 inches. 
         [0041]    Distal to the rear-driving band  111  is a boat tail  113 . In this first preferred embodiment, the conical boat tail  113  is approximately .60-.80 calibers in length and tapers at an approximate angle of 7.0-8.0 degrees to the base  115 , which has an approximate diameter of .8-.9 calibers. The proximal .10 caliber length of the boat tail  113  is engraved by the rifling lands during firing and, thus, also serves to widen the rear-driving band  111  mechanically to an effective width of approximately .80 calibers. 
         [0042]    As further refinement to this first preferred embodiment, the boat tail  113  is preferentially machined or hollowed to form a rear base cavity  117 . This rear base cavity  117  has several functions. It shifts the center of gravity of the rifle bullets slightly forward as compared to bullets having no rear base cavity  117 . This results in better in-flight stability and enlarges the effective volume of each cartridge&#39;s combustion chamber. In this preferred embodiment, the rear base cavity  117  should be drilled axially along the length of the bullet ranging from an approximate depth of .3 calibers to .5 calibers having an approximate 120-degree drill point angle in the rear region of the boat tail  113 . The drill diameter for the bore cavity depends on the bullet caliber, but is selected to leave a thin, but substantial, ring of material, 0.008 to 0.016 inches in rim thickness at the base  115  of the boat tail  113 . 
         [0043]    A second preferred embodiment of this self-aligning bullet design contains those elements set forth in the first preferred embodiment with some additional refinements, now stated. In this second preferred embodiment, the self-aligning bullet has a rear base cavity  117  that is machined to allow for the insertion of a desired core material  119  to bring each bullet design instance to its preferred final weight and mass distribution. When machining the rear base cavity  117 , various drill tip angles and reamer shapes are intended, depending upon the preferential amounts of brass to be removed, the relative density of additional core material  119  to be added in each specific design, and the ability to respond to bullet expansion under stress of firing. The base drill diameter is preferentially selected from drill diameters available. It is disclosed for the selected drill size to establish a preferred rim thickness (0.008-0.016 inches) for each given bullet size or caliber. This second preferred embodiment may preferentially also have an internal relief groove  121  created within the region of the rear-driving band  111 . The internal relief groove  121  may, depending upon preference, have an internal diameter greater than the base drill diameter, thereby creating a preferred difference in depth of the rear base cavity  117 . This may be a preferred depth of 0.0025 inches having potential tapers approximating .1 caliber in length leading into and out from the relief groove. A preferred taper may mimic the external .1 caliber tapers of the rear-driving band  111 . During firing, the internal relief groove  121  serves to compensate for any amount of brass material displaced as the barrel rifling forcibly engraves the rear-driving band  111 . Such displacement may also serve to mechanically enmesh the core material  119 , thereby creating more stability within the bullet. To facilitate the insertion and concentric pressure seating of the core material  119 , a tapered lead-in ramp  123  may be preferentially machined into the distal .1 caliber length of the rear base cavity  117 . The mouth of the rear base cavity  117  may also be enlarged by 0.004 inches in internal diameter in this second preferred design embodiment. 
         [0044]    This disclosure of the two preferred embodiments are not intended as a limitation on the scope of the invention but instead a detailed enabling description of the bullet design advances contemplated herein.