Patent Publication Number: US-2010126371-A1

Title: Projectile wad for ammunition cartridges

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to ammunition cartridges such as shotgun shells and the like. More particularly, the invention relates to projectile wads for ammunition cartridges. 
     2. Description of Related Art 
       FIG. 1  depicts a typical ammunition cartridge  20 , which includes: a tube  24 , a basewad  26 , a metal head  28 , and a projectile wad  44 . An example of such an ammunition cartridge  20  is the WINCHESTER XPERT® shotshell by Olin Corporation, East Alton, Ill. The tube  24  is typically formed of plastic and may be of a type known the Reifenhauser tube. At the aft end  30  of the ammunition cartridge  20 , the basewad  26  is inserted in a tight fitting relation into the aft end of the tube  24 . The cup-shaped metal head  28  surrounds an aft portion of the tube  24  and is crimped to the outwardly-flared aft end of the tube  24  and basewad  26  to mechanically secure the three together and form an annular rim  32 , which is useful to assist in extraction of the ammunition cartridge  20  from a shotgun (not shown). A central aperture  34  in the metal head  28  is co-aligned with a pocket  36  in the basewad to accommodate a battery cup-type primer  38  in press fit relation. The basewad  26  has a forward surface  42  that defines a portion of a powder chamber for receiving a propellant charge  40 . The projectile wad  44  has an aft surface  43  forming an over-powder cup (powder cup), which typically bounds most of the remainder of the powder chamber. In the ammunition cartridge  20  shown in  FIG. 1 , the aft rim  45  of the projectile wad  44  is close to contacting a forward rim  46  of the basewad  26 . Thus, between the aft rim  45  and the forward rim  46 , the powder chamber may be bounded by a cylindrical segment of the interior surface  47  of the tube  24 . 
     In the design of ammunition cartridges, a number of advancements have been made to improve the sealing of combustion gases against infiltration between the basewad  26  and tube  24 . For example, U.S. Pat. No. 6,164,209 to Best et al. (the &#39;209 patent) discloses an ammunition cartridge including a projectile wad having an aft portion located at least partially concentrically within a skirt of the basewad so as to define a powder chamber for containing the propellant charge. Upon firing of the ammunition cartridge, the pressure increase produces a radially outward force on the powder cup, causing the powder cup to expand radially and bear against the basewad to maintain a seal against escape of propellant combustion gasses from the powder chamber. Also, the basewad expands radially to seal combustion gasses against infiltration between the basewad and tube. 
     While the ammunition cartridge design described in the &#39;209 patent is successful in improving the sealing of combustion gasses, room for improvement exists. For example, the ammunition cartridge described in the &#39;209 patent includes a long, thin tapered basewad skirt that is designed to accept the projectile wad powder cup within an open end (mouth). The basewad skirt tapers to a sharp edge at the lip. This sharp edge is delicate and susceptible to damage at numerous points in the manufacturing process and during handling and conveying. It is not uncommon for the lip of the basewad skirt to have several minor dings and dents that cause inward deformation of material. This creates locations for the square edge of the powder cup skirt to catch as it is inserted into the shell, causing the powder cup to tip and seat improperly at an angle. Improper alignment of the powder cup can result in low report on firing and, in extreme cases, a bulge is created in the ammunition cartridge sidewall large enough to prevent chambering in the shotgun. Accordingly, care is taken during the manufacturing process to avoid powder cup misalignment, and any ammunition cartridges having a misaligned powder cup are discarded, which increases the production cost of the ammunition cartridges. 
     BRIEF SUMMARY OF THE INVENTION 
     The above-described and other drawbacks and deficiencies of the prior art are overcome or alleviated by an ammunition cartridge comprising: a tube extending along a central longitudinal axis from an aft end of the tube to a fore end of the tube; a basewad disposed within the tube and located proximate the aft end of the tube; a projectile wad disposed within the tube; a propellant charge disposed within a chamber formed between the basewad and the projectile wad; and at least one projectile disposed within the tube between a forward facing surface of the projectile wad and the fore end of the tube. The basewad includes an interior surface extending outward and forward from a generally forward facing inner portion to a generally inward facing fore portion so as to define a skirt of the basewad. The projectile wad includes an interior surface extending outward and rearward from a generally aft facing inner portion to a generally inward facing aft portion so as to define a powder cup skirt. The powder cup skirt has a chamfer formed around an outer perimeter of a lip of the powder cup skirt, the lip being slidably received within the skirt of the basewad so as to form the chamber between the powder cup skirt and the skirt of the basewad. An end surface of the lip is substantially uninterrupted around the entire powder cup skirt. 
     In one aspect of the present invention, the powder cup skirt has a thickness T B  at a transition point between the outer surface and the chamfer. The thickness T B  is preferably between about 0.015 inches to about 0.028 inches, and more preferably between about 0.018 inches to about 0.024 inches. 
     In various embodiments, the powder cup skirt has an outside diameter of between about 0.690 inches to about 0.712 inches, and more preferably between about 0.695 inches to about 0.710 inches. In various alternative embodiments, the powder cup skirt has an outside diameter of between about 0.580 inches to about 0.600 inches, and more preferably between about 0.585 inches to about 0.595 inches. 
     In various embodiments, the chamfer has a forward facing cone angle of about 18 degrees relative to the central longitudinal axis. The transition point may be about 0.30 inches from an end surface of the lip. The lip may have a thickness of about 0.10 inches at the end surface of the lip. The powder cup skirt may have an outside diameter of between about 0.700 inches to about 0.712 inches. 
     The cartridge may further include a plurality of petals disposed at a perimeter of the forward facing surface, with the projectile being disposed between the plurality of petals. The cartridge may also further include a compressible shock absorbing midsection disposed between the forward facing surface and the interior surface of the projectile wad. A plurality of evenly spaced channels may be disposed along an outer surface of the powder cup skirt. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be more fully understood from the following detailed description taken in conjunction with the accompanying drawings wherein like elements are numbered alike, and in which: 
         FIG. 1  is a longitudinal sectional view of a prior art ammunition cartridge; 
         FIG. 2  is a longitudinal sectional view of an ammunition cartridge according to an embodiment of the present invention; 
         FIG. 3  is a longitudinal sectional view of a basewad of the ammunition cartridge  FIG. 2 ; 
         FIG. 4  is a rear perspective view of the basewad of  FIG. 3 ; 
         FIG. 5  is a front perspective view of the basewad of  FIG. 3 ; 
         FIG. 6  is a partial cross-sectional view of a fore end of the basewad of  FIG. 3 ; 
         FIG. 7  is a side elevation view of a projectile wad of the ammunition cartridge of  FIG. 2 ; 
         FIG. 8  is a front elevation view of the projectile wad of  FIG. 7 ; 
         FIG. 9  is a rear elevation view of the projectile wad of  FIG. 7 ; 
         FIG. 10  is a section view of the projectile wad taken along section B-B of  FIG. 7 ; 
         FIG. 11  is a section view of the projectile wad taken along section A-A of  FIG. 7 ; 
         FIG. 12  is an end view of a vent disposed in a powder cup of the projectile wad taken at detail C of  FIG. 8 ; 
         FIG. 13  is a cross-sectional view of the vent disposed in the powder cup of the projectile wad taken at detail D of  FIG. 10 ; and 
         FIG. 14  is a cross-sectional view of a powder cup skirt having a reduced diameter portion. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 2  depicts an ammunition cartridge  50  according to an embodiment of the present invention. The ammunition cartridge  50  includes: a tube  51  extending along a central longitudinal axis  500  from an aft end  56  to a fore end  59 ; a basewad  52  disposed within the tube  51  and located proximate the aft end  56 ; a projectile wad  92  disposed within the tube  51 ; a propellant charge  96  disposed within a chamber  94  formed between the projectile wad  92  and the basewad  52 ; and at least one projectile  100  disposed within the tube  51  between a forward facing surface  101  of the projectile wad  92  and the fore end  59  of the tube  51 . The basewad  52  includes an interior surface  72  extending outward and forward from a generally forward facing inner portion  74  to a generally inward facing fore portion  76  so as to define a skirt  80  of the basewad  52 . The projectile wad  92  includes an interior surface  71  extending outward and rearward from a generally aft facing inner portion  73  to a generally inward facing aft portion  75  so as to define a skirt  77  on an over-powder cup (powder cup)  90 . The powder cup skirt  77  has a chamfer  81  formed around an outer perimeter of a lip  57  of the powder cup skirt  77 , which allows the powder cup skirt  77  to be slidably received within the skirt  80  of the basewad  52  to form the chamber  94 . As will be discussed in further detail hereinafter, the chamfer  81  minimizes the problems previously associated with the powder cup skirt  77  catching on the basewad  52  by providing a clearance between the edges of the powder cup skirt  77  and the skirt  80  of the basewad  52 . 
     The ammunition cartridge  50  has a hull including the tube  51 , the basewad  52 , and the metallic head  53 . The hull may be as described in U.S. Pat. No. 6,164,209 to Best et al., which is incorporated by reference herein in its entirety. It is contemplated, however, that other hull designs may be used. For example, hulls such as those found in commercially available WINCHESTER AA® shotshells may be used. The tube  51  is of conventional construction and may be formed of paper or plastic (e.g., polyethylene). The head  53  may similarly be of conventional construction and may be formed of steel or brass. The tube  51  has interior and exterior predominately cylindrical surfaces  54  and  55  respectively. A foremost portion  58  of the tube  51  forms a crimp enclosing a fore end of the ammunition cartridge  50 . 
     Proximate the aft end  56  of the tube  51 , the basewad  52  is contained within the tube  51 . A lateral, longitudinally-extending, generally cylindrical, exterior surface  60  of the basewad  52  engages the interior surface  54  of the tube  51  in direct contact along a length thereof. 
     The head  53  is unitarily formed having a sleeve portion  61 , an interior surface  62  of which contacts the exterior surface  55  of the tube  51 . At its aft end, the sleeve portion  61  flares outward to form a rim of the ammunition cartridge  50  which compressively holds an outwardly flared aft portion of the tube  51  to a beveled shoulder or lip  64  of the basewad  52 . A web portion  66  of the head  53  spans the sleeve portion  61  at the aft end thereof, extending inward from the rim to form a base of the ammunition cartridge  50 . The web portion  66  has a central aperture  67  proximate which the web portion  66  is deformed forwardly. The web portion  66  contacts an aft or base surface  68  of the basewad  52 . 
     The basewad exterior surface  60  is of a diameter effective to maintain itself in engagement with the interior surface  54  of the tube  51 . By way of example, the ammunition cartridge  50  of  FIG. 2  may have proportions generally corresponding to an embodiment as a 12 gauge ammunition cartridge. In the exemplary  12  gauge ammunition cartridge embodiment, the exterior surface  60  has a diameter of about 0.74 inches. As shown in further detail in  FIG. 3 , the interior surface  72  of the basewad  52  extends from the generally forward facing inner portion  74  forward and outward to the generally inward facing fore portion  76 . An annular frustoconical bevel surface (chamfer)  78  meets the exterior surface  60  at an annular vertex  79  defining a rim at the forward extremity of the basewad  52 . The chamfer  78  thus connects the fore portion  76  to the exterior surface  60 . The interior surface  76 , exterior surface  60  and chamfer  78  bound the skirt  80  of the basewad  52 . Extending forward from a central aperture in the aft surface  68  is a primer pocket  82  formed by a stepped primer pocket surface  84 . When the hull is assembled as shown in  FIG. 2 , a primer, such as a battery cup-type primer  86 , extends through the central aperture  67  of the head  53  and into the primer pocket where the primer  86  is firmly engaged by the primer pocket surface  84 . 
     Surrounding a fore end of the primer pocket  82 , the basewad  52  includes a hub  104  bounded internally by the primer pocket surface  84  and externally by the inboard wall of an annular, generally forward-facing, channel  106 . The channel has a bottom  108  located aft of the forward surface or rim  110  of the hub by a channel depth D. 
     In the example shown in  FIG. 3  and in further detail in the perspective view of  FIG. 4 , the basewad has a plurality (e.g., eight in the illustrated embodiment) of blind compartments  120 . The compartments  120  are open to the aft surface  68  and extend forward therefrom. The compartments  120  are located on the boundary between a rearwardly projecting central portion  122  of the aft surface  68  surrounding an opening to the primer pocket and an outer portion  124  of the aft surface extending radially outward from the central portion  122  and forwardly offset therefrom. In the illustrated embodiment of  FIG. 3 , the compartments  120  do not reach the basewad exterior cylindrical surface  60 . Optionally, the compartments may be formed entirely or partially as channels open to the basewad exterior surface  60 . In alternative arrangements, the blind compartments  120  may be eliminated. 
     Returning to  FIG. 2 , there can be seen details of the skirt  80  of the basewad  52  and its interaction with the powder cup  90 . A nearly cylindrical exterior surface  136  of the powder cup  90  is in substantially continuous circumferential contact with a first interior surface portion  138  of the fore portion  76  of the basewad interior surface  72 . Details of the first surface portion  138  can be seen in  FIGS. 5 and 6 . The first surface portion  138  extends aft from an annular junction  139  with the chamfer  78 . The first surface portion  138  extends aft to a second annular junction  140  with a second surface portion  142 . The first surface portion  138  is substantially frustoconical with a fore-to-aft taper β ( FIG. 6 ) measured as an overall forward facing cone angle between the surface and the longitudinal direction (e.g. axis  500 ). Advantageously, β is quite small, preferably less than three degrees, more preferably about two degrees or less, and minimum values for β may be minimum values effective to provide releaseability from a mold. This narrow range of the angle β is advantageous to allow proper telescoping of the powder cup  90  within the basewad  52 , while other angles are less sensitive. For example, the chamfer  78  has a fore-to-aft taper angle θ of about thirty degrees in the exemplary embodiment. This angle is sufficiently small to guide insertion of the powder cup  90  into the basewad  52  when the ammunition cartridge  50  is loaded. The angle θ (and associated therewith, the wall thickness of the skirt  80  near the rim  79 ) is, however, large enough so that the skirt  80  is sufficiently robust to withstand loading, discharge, and, preferably, reloading. A broader exemplary range for θ is from about 20° to about 45°. Specifically, at the junction  139 , the skirt  80  has a wall thickness t. In the exemplary embodiment, the thickness t is about 0.015 inches. Given the shallow angle β, the wall thickness does not greatly increase along the first portion  138  extending to the second junction  140  at a distance L 1  from the rim  79 . For example, with an exemplary distance L 1  of 0.20 inches and an angle β of one degree, the wall thickness increases only to about 0.018 inches at the second junction  140  from the wall thickness t of 0.015 inches at the first junction  139 . 
     Proceeding aft from the second junction  140 , the fore-to-aft taper further increases. In the exemplary embodiment, the second surface portion  142  has a taper angle γ ( FIG. 6 ). As discussed in further detail below, the angle aft of the powder cup-engaging portion of the basewad may vary significantly based upon the application for which the basewad is designed. An exemplary angle γ for a basewad defining a relatively voluminous powder chamber is about seven degrees as shown in the embodiment of  FIG. 6 . In the illustrated embodiment, the second surface portion  142  extends aft from the second junction  140  to a third junction  143  with a curving portion  144  of the interior surface along which the taper further increases. 
     Referring now to  FIG. 7 , a side elevation view of the projectile wad  92  is shown. The projectile wad  92  includes three main portions: the powder cup  90 , the compressible mid section  103 , and a projectile cup  200 . The projectile wad  92  is preferably a unitary structure made from plastic (e.g., polyethylene). 
     The mid section  103  is attached to a forward facing surface  202  of the powder cup  90 . The mid section includes a plurality of spring members  204 , which in this embodiment are in the form of collapsible columns. The spring members  204  include bent portions  206  that allow the columnar spring members  204  to buckle during loading to provide compensation for variations in load volumetric fit (e.g., variations in the projectile or powder charge). Hinge compressibility of the spring members  204  also helps optimize ballistic performance and absorb shock load, which is transmitted substantially in the direction of longitudinal axis  500 . 
     The projectile cup  200  includes an aft facing surface  208 , which is attached to the forward ends of the spring members  204 . The projectile cup  200  also includes the forward facing surface  101  upon which one or more projectiles (e.g., a slug or shot) rests in the fully-assembled ammunition cartridge  50  ( FIG. 2 ). Extending forwardly from the surface  101  are a plurality of petals, which cooperate to form sides of the projectile cup  200 .  FIG. 7  depicts the shot-wad  92  in an unloaded condition, outside of the tube  51 . As can be seen in  FIG. 7 , the petals are angled outwardly relative to the planar surface  101 . Upon insertion of the projectile wad  92  into the tube  51 , an outside surface  212  of each of the petals  210  contacts the interior surface  54  ( FIG. 1 ) of the tube  51  and the petals  210  are straightened such that the outside surfaces  212  of the petals  210  are generally perpendicular to the surface  101 .  FIG. 8  is a front elevation view of the projectile wad  92  showing the petals  210  extending from the surface  101 . 
     As can be seen in  FIG. 7 , the powder cup  90  is defined by the interior surface  71 , which extends outward and rearward from the generally aft facing inner portion  73  to the generally inward facing aft portion  75  so as to define the skirt  77 . Disposed around the outer perimeter of the lip  57  of the skirt  77  is the chamfer  81 . As can be seen in  FIGS. 7 and 9 , a plurality of equally-spaced channels  214  are disposed in an outside surface  214  of the skirt  77 . In the embodiment shown, four channels  214  are disposed in the outside surface  214 . The channels  214  act as air vents to prevent the buildup of air pressure in the chamber  94  during the loading process, when the powder cup skirt  77  is being inserted in the skirt  80  of the basewad  52  ( FIG. 1 ). 
     Referring now to  FIG. 10 , a transverse section view of the mid portion  103  is shown. As can be seen in  FIG. 10 , four spring members  204  are used. Two of the spring members  204  are located near the center of the surface  202 , and the remaining two larger spring members are located near the perimeter of surface  202 . The arrangement, size, and location of the spring members  204  may be selected based on the amount of compressibility or shock absorption desired. 
     Referring to  FIG. 11 , a longitudinal section view of the projectile wad  92  is shown. The powder cup  90  has an outer surface  216 , which has a diameter, indicated at D B  effective to maintain itself in engagement with the first interior surface portion  138  of the fore portion  76  of the basewad interior surface  72  ( FIG. 3 ) while allowing the powder cup skirt  77  to be slidably received within the skirt  80  of the basewad  52 , as shown in  FIG. 2 . For example, in the exemplary  12  gauge ammunition cartridge embodiment, the powder cup  90  preferably has a diameter D B  of between about 0.690 inches to about 0.712 inches, and more preferably between about 0.695 inches to about 0.710 inches. In another example, for a 20 gauge ammunition cartridge embodiment, the diameter D B  is preferably between about 0.580 inches to about 0.600 inches, and more preferably between about 0.585 inches to about 0.595 inches. 
     It has been determined that the ability of the powder cup skirt  77  to adequately seal combustion gasses within the chamber  94  is largely dependent upon the powder cup skirt  77  thickness, indicated at T B , at the transition point between the outer surface  216  and the chamfer  81 . Preferably, the thickness T B  is between about 0.015 inches to about 0.028 inches, and more preferably between about 0.018 inches to about 0.024 inches. Surprisingly, it has been determined that these thicknesses are applicable to both 12 and 20 gauge embodiments, regardless of the outside diameter D B . 
     In the exemplary  12  gauge ammunition cartridge embodiment: the overall length of the projectile wad  92 , indicated at L A , may be between about 1.685 inches to about 1.655 inches; the length of the petals  210 , indicated at L B , may be between about 0.795 inches to about 0.775 inches; the distance between surfaces  73  and  101 , indicated at L c , may be about 0.735 inches; the length of spring members  204 , indicated at L D , may be about 0.530 inches; and the distance between surfaces  208  and  73 , indicated at L E , may be about 0.655 inches. The petals  210  preferably have a thickness T A  of between about 0.017 inches to about 0.023 inches. The projectile cup  200  (with petals  200  in the closed, loaded position) may have the same outside diameter as the outside diameter D B  of the projectile wad  92 . 
     In the exemplary  20  gauge ammunition cartridge embodiment: the overall length of the projectile wad  92 , indicated at L A , may be about 1.695 inches; the length of the petals  210 , indicated at L B , may be about 0.830 inches; the distance between surfaces  73  and  101 , indicated at L c , may be about 0.690 inches; the length of spring members  204 , indicated at L D , may be about 0.520 inches; and the distance between surfaces  208  and  73 , indicated at L E , may be about 0.620 inches. The petals  210  preferably have a thickness T A  of about 0.031 inches. The projectile cup  200  (with petals  200  in the closed, loaded position) may have the same outside diameter as the outside diameter D B  of the projectile wad  92 . 
     Referring to  FIG. 12 , a detailed end view of the lip  57  of the powder cup skirt  77  is shown. As can be seen in  FIG. 12 , the vent  214  extends into the outer surface  216  to a depth d, which is less than the thickness T B  of the powder cup skirt  77 . The vent  214  is defined by a substantially planar base surface  300  and outwardly extending side surfaces  302 . The width of base surface  300  is indicated at W B  and the overall width of the vent  214  is indicated at W v . Disposed behind the vent  214  at the aft portion  75  of skirt  77  is an increased thickness portion  304 , which acts to prevent the skirt  77  from splitting along the channel  214 . The increased thickness portion  304  has a thickness indicated at t. The width W B  is preferably about 0.30 inches; the width W v  is preferably about 0.062 inches; the depth d is preferably between about 0.008 to about 0.012 inches; and the thickness t is preferably about 0.005 inches. 
     Referring to  FIG. 13 , a detailed side section view of the lip  57  of the powder cup skirt  77  is shown. As can be seen in  FIG. 13 , the chamfer  81  has a forward facing cone angle, indicated at λ of about 18 degrees relative to the outer surface  216  of the skirt  77 . The chamfer  81  is separated from the aft portion  75  of skirt  77  by an end surface  306  of the lip  57 . Preferably, the transition point between the outer surface  216  and the chamfer  81  is at a distance from the end surface  306 , as indicated at L F , equal to about 0.030 inches. These dimensions provide a clearance at the lip  57 , as indicated at d, of about 0.010 inches, which helps to insure undisturbed entry of the lip  57  into the basewad  52  mouth without catching on any deformations in the basewad  52  mouth. Accordingly, the chamfer  81  helps to ensure that the powder cup  90  remains in proper alignment when the powder cup skirt  77  is slidably inserted into the basewad  52  mouth during the loading process. As a result, the chamfer  81  alleviates problems associated with improperly aligned powder cups, such as low report on firing and bulges in the ammunition cartridge  50  sidewall that can prevent chambering in the shotgun. 
     Also, in the embodiment of  FIGS. 9 ,  12 , and  13 , the end surface  306  of the lip  57  is substantially uninterrupted around the skirt  77 . That is, the end surface  306  of the lip  57  is substantially free of any notches or slots. It has been surprisingly found that the substantially uninterrupted end surface  306  allows for improved powder cup  90  alignment compared to projectile wads having an end surface  306  that is slotted or notched. 
     Referring to  FIG. 14 , a detailed side section view of the lip  57  of the powder cup skirt  77  is shown wherein the forward portion of the powder cup skirt  77  has a reduced outside diameter area, with the reduced outside diameter being indicated at D reduced . The reduced outside, diameter area minimizes the interference fit between the outer surface  216  of the powder cup  90  and the first interior surface portion  138  of the fore portion  76  of the basewad interior surface  72  ( FIG. 3 ) to prevent bulging at the outside of tube  51  in this vicinity. 
     Referring again to  FIG. 2 , the propellant  96  may be any propellant suitable for the desired application of ammunition cartridge  50 . Suitable propellants include, for example, the WINCHESTER SUPER-TARGET® and SUPER-FIELD® lines of BALL POWDER® smokeless propellant of Olin Corporation, East Alton, Ill. (BALL POWDER being a trademark used under license from Primex Technologies, Inc., St. Petersburg, Fla.). 
     The projectile  100  may be any one or more projectiles suitable for the desired application of ammunition cartridge  50 . For example, projectile  100  may include a single slug or multiple shot formed from any suitable material (e.g., lead). Other examples of projectiles  100  include non-lethal projectiles such as: a solid rubber slug or multiple rubber shot; a liquid filled projectile having an elastomeric or other flexible casing surrounding a liquid core; a plurality of solid particles encased in an elastomeric or otherwise flexible cover or casing (e.g. a “bean bag” filled with a powder, granules, pellets and the like); a projectile having a sponge or other solid foam tip extending forward from a relatively solid and rigid body; a projectile having an elastomeric or other flexible casing surrounding a foam core; and wooden slugs and batons. 
     Prior to firing of the ammunition cartridge  50 , the propellant charge  96  is substantially encapsulated by a combination of the powder cup  90 , basewad  52 , and primer  86 . Preferably, none of the propellant is in direct contact with the tube  51  or, more particularly, its interior surface  54 . Such encapsulation helps prevent sifting of the powder out of the chamber  94  and between the basewad  52  and the tube  51 . Such encapsulation may also help to prevent moisture infiltration into the chamber  94 . In firing the ammunition cartridge  50 , when the user causes the primer  86  to ignite and, thereby, ignite the propellant  96 , pressure within the powder chamber  94  greatly increases. Such pressure produces a forward force on the powder cup  90 , tending to drive the powder cup  90  forward, out of the basewad  52 . After an initial compression of the midsection  103  (if any), forward movement of the powder cup  90  is translated to the projectile cup  200 , tending to propel the projectile wad  92  and projectile(s)  100  forward, out of the hull and down the barrel of the shotgun. The pressure increase also produces a radially outward force on the powder cup  90  particularly adjacent to the lip  57  of the powder cup skirt  77 . Such radially outward force strains the powder cup  90  causing the powder cup  90  to expand radially and bear against the first surface portion  138  of the basewad  52 , the interior surface  54  of the tube  51 , and gun barrel, thereby maintaining a seal against escape of propellant combustion gases. 
     Given the compliance of the basewad  52 , such radially outward force also causes the basewad  52  (particularly proximate the forward rim  79  thereof) to expand radially into firm(er) engagement with the interior surface  54  of the tube  51 . This firm engagement is believed to help resist the rearward infiltration of combustion gases between the basewad  52  and tube  51  once the powder cup  90  has disengaged from the basewad  52 . 
     Additionally, when the ammunition cartridge  50  is fired, the pressure within the powder chamber  94  extends within the channel  106 , pressing the hub  104  radially inward, causing the adjacent portion of the primer pocket surface  84  to bear more firmly against the primer  86  reducing the probability of combustion gas infiltration between the primer  86  and the primer pocket surface. 
     The advantages of the present invention will become apparent from the examples that follow. The following examples are intended to illustrate, but in no way limit the scope of the present invention. 
     EXAMPLES 
     In a first comparative example, 12 gauge ammunition cartridges were manufactured with a 1⅛ ounce wad similar to the 12-gauge configuration described hereinabove with the exception that in the ammunition cartridges of the first comparative example four gaps were disposed through the chamfer, 90 degrees apart and in line with air vents on the powder cup. Each of the air vents extended from the inward facing aft portion  75  through the chamfer and defined a notch in the end surface  306  of the powder cup  90 . Approximately 35 million projectile wads of this design were used in production field loads. The 12 gauge ammunition cartridges of the first comparative example provided little improvement in the frequency of tipped powder cups for loads over that obtained with non-chamfered powder cups of the prior art. 
     In a second comparative example, 12 gauge ammunition cartridges were manufactured with a 1⅛ ounce wad similar to the 12-gauge configuration described hereinabove with the exception that the powder cup skirt thickness T B  was increased to between 0.028 inches and 0.032 inches with a powder cup skirt diameter D B  between 0.692 inches and 0.702 inches. The 12 gauge ammunition cartridges of the second comparative example provided unacceptable occurrences of low reports on firing, even with properly seated projectile wads. While not wanting to be bound by theory, it is believed that powder cup skirts with a thickness T B  of greater than 0.028 inches are less effective than thinner powder cup skirts in sealing propulsion gasses because of the decreased pliability of the skirt. The reduced outer diameter and decreased pliability in the powder cup skirts of the second comparative example does not allow sufficient radial expansion of the powder cup skirt as the wad travels down the shell and gun barrel to maintain a seal against escape of propellant combustion gases. 
     In a first example of an embodiment of the present invention, 12 gauge ammunition cartridges were manufactured with a 1⅛ ounce projectile wad in accordance with the 12-gauge configuration described hereinabove. 5000 rounds were shot at 70 degrees with no wad-related problems. Approximately 120 rounds were shot at 70, 125, 20 and 0 degrees for wad recovery, with no defects found. Only one shell was found to have a misaligned wad, which was found to be caused by a deformation in the basewad mouth. This one defective shell accounted for only 0.01% of the shells produced with the 1⅛ ounce projectile wad in accordance with the 12-gauge configuration described hereinabove. Historically, misaligned projectile wads account for a 0.029% to 1% defect rate where non-chamfered, prior art projectile wads are used. In conclusion, it is believed that this testing shows ballistic performance of this first example to be equivalent to the ballistic performance provided by the non-chamfered, prior art projectile wads, while the frequency of misaligned projectile wads is significantly lower. 
     Although one or more embodiments of the present invention have been described, it will nevertheless be understood that various modifications may be made without departing from the spirit and scope of the invention. For example, the dictates of particular end uses may influence certain parameters of the projectile wad as well as the remainder of the ammunition cartridge. Also, adaptations may be made relative to the type of ammunition cartridge to which the projectile wad of the invention is applied (e.g., gauge and shell length). Thus, the principles of the invention may be applied to shells other than those illustrated, for example, to 8-gauge shells used in industrial applications. Accordingly, other embodiments are within the scope of the following claims.