Abstract:
Disclosed is a double stack box magazine for rimmed ammunition cartridges of varied lengths. It includes a housing having a neck portion in which cartridges are arranged in a single column, a double-stack portion in which cartridges are arranged in laterally alternating columns, and a transition portion between the neck portion and the double-stack portion. A pair of rim clearance channels is provided, on opposed interior lateral surfaces of the housing. A first channel portion allows clearance for cartridge rims without respect to forward and rearward position of the cartridges within the housing, which may vary depending on individual cartridge length. A second channel portion in the neck provides an abutment against which laterally opposed areas of a cartridge rim bear to shift the cartridge to a rearward position. A third channel portion provides transition between the first and second channel portions.

Description:
RELATED APPLICATION 
       [0001]    This application claims priority to my U.S. Provisional Patent Application No. 61/383,848 filed Sep. 17, 2010 entitled Double Stack Box Magazine for Shotgun Cartridges. 
     
    
     TECHNICAL FIELD 
       [0002]    This application relates to box-type ammunition magazines, particularly to detachable multiple column (double stack) magazines for rimmed cartridges. 
       BACKGROUND 
       [0003]    Typically, ammunition magazines for firearms fall into two broad categories: fixed and detachable. Box magazines may fall into either of these categories. 
         [0004]    Rimmed cartridges present certain challenges for designing and manufacturing reliable ammunition feeding devices, particularly for higher capacity box magazines, not encountered with rimless cartridges. The most popular types of rimmed ammunition include shotgun shells and rimfire cartridges, the latter being used in rifles and pistols. 
         [0005]    Unlike rifle and pistol ammunition which has a very consistent standardization in length of a live cartridge from most manufacturers and/or loads, shotgun ammunition typically has significant variations in live cartridge length from one manufacturer and/or load to the next. The spectrum of length variation for rifle and pistol ammunition can typically be measured in the hundredths of an inch (0.0X0″) if not the thousands of an inch (0.00X″). The spectrum of shotgun ammunition can in some cases be measured at over an inch (X.00″) of length difference from one manufacture to the next. And more typical in the tenths of an inch (0.X00″). 
         [0006]    Manufacturers typically call out shotgun ammunition in ¼ inch (0.25″) or ½ inch (0.5″) increments, for example, 2¾″, 3″, and 3½″. Typically, if a rifle or pistol cartridge has this much difference in length, it becomes a totally different round. For example; 9 mm Luger vs. .380 Auto, .45 Auto vs. .45 GAP, .22 Magnum vs. .22 Long Rifle vs. .22 Short, 8 mm Mauser (7.92×57) vs. 7.92×33 Kurz. Different shotgun models can typically fire everything it is chambered to (in a particular gauge) and all cartridges of shorter length. For example, the typical 12 ga shotgun that is chambered in 3″ can fire both 3″ and 2¾″ cartridges. The typical rifle or pistol model cannot do this safely and/or reliably, the few exceptions not being relevant to this discussion. 
         [0007]    Although shotgun cartridges are typically called out in nominal ¼ inch length increments, they still greatly vary from one manufacturer and/or load to the next. Typically, the length call out is the length of the empty casing or hull. Typically, when it is loaded it loses length from crimping or rolling the casing/hull. Depending on the manufacturer and/or load, a live 2¾″ cartridge can measure less than 2.25″ in length or it can measure more than 2.55″ in length. 
         [0008]    Another difference is that the typical shotgun ammunition is a rimmed cartridge. Most pistol and rifle ammunition has evolved into a rimless cartridge, the exceptions, again, not being relevant to this discussion. The feeding of a double stack of rimless rifle or pistol cartridges in a box magazine does not typically encounter the problem of misaligned rims. 
         [0009]    Box magazines achieve reliability by repeatability. A typical box magazine fed weapon uses an ammunition cartridge that is very consistent in length. This prevents front to back movement and misalignment of the cartridges in the magazine under forceful movement or recoil of firing the weapon. Magazine fed weapons have an optimal position of the next cartridge to load from the top of the magazine. For example, if the cartridge is not contained or restrained to prevent longitudinal (forward and aft) movement, the round can be positioned too far forward in the magazine as it is presented for chambering, causing misalignment, or can prematurely extract from the magazine. This results in a high probability of jamming during chambering of the cartridge. For typical shotgun cartridges, it can also allow the rim of a cartridge below the top cartridge to bind the rim of the top cartridge and cause a jam (failure to feed). 
         [0010]    A box magazine for a shotgun presents a greater challenge because of the rim and shotgun cartridges&#39; wide range of loaded length. For this reason, there are very few box magazine fed shotguns. In the past, box magazines for shotguns have addressed this issue in only two ways, both of which include an upwardly angled stack provided by the follower. Either the cartridge was contained by holding the cartridge by its rim for the length of the magazine, preventing longitudinal movement (particularly forward movement of lower cartridges) and misalignment of cartridges and their rims. Or, it has restrained longitudinal movement (and resulting misalignment) by walls that bear against the head and forward end of the cartridge. This latter solution eliminates the use of all cartridges other than a very small portion of the spectrum of cartridge lengths. This includes many cartridges of the same nominal (call out) length. For example, not all 2¾″ cartridges would fit and/or feed reliably with this method. This is not very feasible considering the wide range of lengths of shotgun cartridges. Moreover, the shooter who is very accustomed to the versatility in the typical shotgun model to except these different lengths of cartridges does not find this acceptable. 
         [0011]    Putting two columns of rimmed shotgun cartridges side by side makes it impossible to contain the cartridges by holding their rims in alignment. The side of the rim toward the transverse center width of the magazine (inboard side) meets the column of cartridges beside it and cannot be contained. Therefore, longitudinal movement (particularly forward movement of a lower cartridge) and misalignment and binding of rims are possible—and likely. 
       SUMMARY OF THE INVENTION 
       [0012]    The present invention provides a new and better way of addressing this problem. A double stack box magazine may taper to a single stack feed at the top. In the double-stack portion, the rounds are allowed to shift forward and rearward without regard to head or rim position. Once single stack geometry is met, an angled surface on the inside of the magazine body catches both sides of the rim of the cartridge and pulls it back to the rear of the magazine, allowing proper alignment and preventing the rims from binding during feed. 
         [0013]    This allows a very large variation of cartridge lengths, both within or beyond the same nominal length, to be fed reliably from the same magazine. That is, not only can cartridges of varying actual lengths within the same nominal size (such as 2¾″) due to variation in manufacturer and/or load be mixed in the same magazine, cartridges of different nominal length (length call out, such as 3″) can be mixed in the same magazine (such as 2¾″ and 3″, up to the maximum chamber length of the shotgun) without loss of feed reliability. Because only one side of a cartridge rim at a time can engage a slot or groove on the inside surface of the magazine body when the shells are in alternating columns, if the front-to-rear dimension of the magazine body is sized to accept shells of varying lengths, the rims cannot reliably be held in alignment against the recoil forces of firing the shotgun or other vibration, sudden movement, or impact. The interior angled surface guides the rim of the uppermost cartridges to the rear, no matter how the shell has become situated during its travel up the magazine body, and places the rim of upper cartridges in front of the rim of the next cartridge below it. 
         [0014]    Alternatively, an insert can be used to take up the excess opening in the front of the magazine. This is less desirable because many different thicknesses of inserts would be needed to meet the same length capabilities as the primary. The followers would have to be switched out along with the inserts to account for the front to back shortening and lengthening of the magazines&#39; interior. This would also sacrifice the ability to load 2¾″ and 3″ shotgun shells in the same magazine and would be less convenient or likely would not be well accepted by the shooter to have to swap out parts in the magazine. 
         [0015]    Another feature of the present design is a follower that is guided in front and rear (rather than lateral) tracks. This allows for a short, one-piece follower that maintains a consistent location as well as consistent force. A one-piece side tilting follower design, like used in many double stack pistol magazines, is possible, but does not offer the same consistency. Any inconsistencies can make jamming more likely. A side tilting design would have to tilt to the side as the follower transitioned between the single and double stack portions of the magazine, while at the same time maintaining the location and angle of the shells resting against the changing angles of the follower. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    Like reference numerals are used to indicate like parts throughout the various figures of the drawing, wherein: 
           [0017]      FIG. 1  is a pictorial view of a double-stack detachable box magazine for shotgun cartridges according to a preferred embodiment of the present invention; 
           [0018]      FIG. 2  is a pictorial view of the magazine shown in  FIG. 1  from an alternate angle; 
           [0019]      FIG. 3  is a pictorial exploded view thereof; 
           [0020]      FIG. 4  is a sectional view taken substantially along line  4 - 4  of  FIG. 2 ; 
           [0021]      FIG. 5  is a lateral sectional view taken substantially along line  5 - 5  of  FIGS. 2 and 4 ; 
           [0022]      FIG. 6  is a view identical to that of  FIG. 5  except that the ammunition cartridges and spring have been removed for clarity; 
           [0023]      FIG. 7  is a cross-sectional view taken substantially along the line  7 - 7  of  FIGS. 5 and 6 ; 
           [0024]      FIG. 8  is a pictorial view of the follower; 
           [0025]      FIG. 9  is an enlarged view of the upper portion shown in  FIG. 5 ; 
           [0026]      FIG. 10  is a cross-sectional view taken substantially along line  10 - 10  of  FIGS. 5 and 6 ; 
           [0027]      FIGS. 11-13  are sequential pictorial views of an upper end of the magazine showing sequential positions of ammunition cartridges being moved upwardly through the magazine body. 
       
    
    
     DETAILED DESCRIPTION 
       [0028]    Referring to the various figures of the drawing and first to  FIGS. 1 and 2 , therein is shown at  10  a magazine according to a preferred embodiment of the present invention. Referring now also to  FIG. 3 , which is an exploded view of the various parts of the magazine  10 , it includes a magazine body  12 , a attached metallic member  14 , which provides feed lips  16  and snaps in place at an upper end of the magazine body  12 . Also shown is a follower  18 , a coil compression spring  20 , a floor plate guide  22 , and a floor plate  24 . As is standard with any box magazine, it is assembled by inserting the follower  18  through an opening  26  at a bottom end  28  of the magazine body  12 . 
         [0029]    A coil spring  20  is inserted through the bottom opening  26  behind or along with the follower  18 . The spring  20  may have a rectangular shape (as shown), may be a cylindrical coil (not shown), or a combination of both, and its width or diameter may be tapered in cross-section along its length. In the present invention, it has been found useful to have a floor plate guide  22  with protrusions  30  or other means for holding the spring  20  in a properly centered position at the lower end. The floor plate guide  22  is inserted into the bottom opening  26  behind or along with the spring  20  and then the floor plate  24  is slid into a closed position by engaging the lateral grooves  32  on lateral rails  34 , which are adjacent the bottom opening  26  of the magazine body  12 . 
         [0030]    For purposes of illustration only, the magazine  10  shown and described herein is adapted to fit a Kalashnikov-pattern Saiga  12  semi-automatic shotgun, manufactured in Russia by Izhmash. Accordingly, the upper end  36  of the magazine body  12  is configured to properly engage a detachable coupling with a magazine well in such a shotgun (not shown). Accordingly, the illustrated embodiment includes a attached metallic member  14  that snaps in place adjacent the upper end  36  of the magazine body  12  to provide durable feed lips  16  in accordance with the existing designs found in a single-stack, smaller capacity box magazine for such a shotgun. Alternatively, feed lips may be provided integrally with the magazine body  12  either from the same material or by encapsulating/over-molding a metallic member. 
         [0031]    Referring now to  FIG. 4 , which shows a vertical sectional view of the magazine  10 , it can be seen that the magazine body  12  has three distinct regions: an upper or neck portion  38 ; a transition portion  40 ; and a widened double-stack portion  42 . The upper or neck portion  38  at the upper end  36  of the magazine body  12  is dimensioned as a single-stack magazine to fit within the magazine well of the shotgun. The standard magazine well of currently-available semi-automatic shotguns cannot accept the added width of a double-stack magazine body. In the prior art, the need for this narrowed neck portion has presented a challenge in that the same follower must move a double row of cartridges along the wider double-stack portion and then completely push all cartridges through a transition to a narrow neck and fully into a delivery position. In the past, this problem has been addressed by either using a follower of exaggerated length, which consumes a greater portion of the magazine&#39;s length, or using hinged follower arms that displace into a more narrow profile as they enter the neck portion of the magazine, creating a complex and expensive-to-construct design. The present invention addresses this issue differently, as will be more fully explained below. 
         [0032]    As discussed in the background section above, reliably feeding shotgun shells in a box magazine presents challenges not found in handling rifle and pistol cartridges. Generally, a shotgun is expected to be able to handle and fire shells of the specified chamber length or shorter. Moreover, shells of any standard nominal length may vary considerably in actual length. Prior art box magazines rely on the length of each cartridge being substantially identical, within a very small acceptable tolerance and/or use of a significantly angled follower. Also as described above, prior single-stack box magazines for shotgun shells address this challenge by engaging the rim of each cartridge on both sides within a narrow track or groove that maintained rims of subsequent cartridges in an “ordered” position and use a significantly angled follower to prevent binding caused by frontward/rearward shift to provide reliable feeding into a position to be stripped away by the shotgun&#39;s reciprocating bolt. 
         [0033]    Referring now to  FIGS. 5 and 6 , therein are shown sectional views taken substantially along the lateral longitudinal center of the magazine  10 .  FIG. 5  shows the magazine  10  partially loaded with shotgun shells  44 , which are also sectioned in this view.  FIG. 6  is substantially the same as  FIG. 5 , except that the shotgun shells  44  have been removed from the view, along with the spring  20  for clarity. The follower  18  is shown in the same position in each view, however. These views show the lateral interior surface  46  of the magazine body  12 . The opposed lateral surface (not shown in these views) is configured identically in a mirror image. Alternatively, the position of certain components can be vertically offset in one side relative to the other in order the balance the handling of the staggered double columns of shells  44 . 
         [0034]    Adjacent the rear edge of the magazine body  12  is a relatively wide rim clearance channel  48 . A rear edge  50  of the channel  48  is defined along the rearward interior surface of the magazine body  12 . A forward edge  52  of the channel  48  is defined by the lateral interior surface  46 . In preferred form, however, the forward edge  52  is positioned to accommodate even the shortest nominal or actual length shotgun shells  44  without confronting the rim. 
         [0035]      FIG. 7  shows a cross-sectional view taken substantially along line  7 - 7  of  FIGS. 5 and 6 , and illustrates the relative lateral depth of the rim clearance channel  48  and lateral interior surfaces  46 . If desired, the lateral interior surface  46  may be inlet with a recessed area  54  in order to reduce material and weight from the magazine body  12  and/or to reduce frictional surface area between the interior surface  46  and the shells  44 . If such a recessed area  54  is included, adjacent portions of the lateral interior surface  46  on each side of the magazine body  12  should be maintained in substantially the same plane in order to smoothly guide the bodies of shotgun cartridges or shells  44  as they slide along the length of the magazine  10 . The recessed area  54  can be configured to act as an additional follower guide when the follower  18  is in the upper portion  38  of the magazine body  12  or to provide an alternate follower stop. Alternatively, the recessed area  54  can be configured to function as a guide for round spring (not shown). 
         [0036]    The overall front-to-rear interior dimension  56  should be configured to accept the longest expected overall length of a shotgun cartridge  44  to be used in the magazine  10  and its associated shotgun (not shown). The front-to-rear dimension  58  of the rim guide channel  48  optimally may be selected such that the rim of a shotgun shell of the shortest expected overall length will remain between rear and forward edges  50 ,  52  of the clearance channel  48  when a shell is shifted forward to the point of being against or near the forward interior surface  60  of the magazine body  12 . 
         [0037]    It can be appreciated by comparison of the views in  FIGS. 4 and 7  that while in the double-stack portion  42  of the magazine body  12 , the alternating rows of shotgun shells  44  have their respective rims engaged in only one of the laterally opposed rim guide channels  48 . Because only a very minor portion of the cartridge rim could be engaged in the clearance channel  48  in the double-stacked portion  42  of the magazine  10 , it has been found that the rearward shock forces to which an attached magazine  10  is subjected when the shotgun is fired (or even when dropped or otherwise impacted) is likely to jar the cartridges  44  out of a narrow guide channel until the cartridge comes to rest against the forward interior surface of the magazine. Thus, the present design allows this inevitable movement to occur, while maintaining containment of a rim portion of each cartridge  44  in one of the relatively wide rim clearance channels  48 . 
         [0038]    The follower  18  has forward and rearward guide rails  62 ,  64 , which engage forward and rearward follower guide channels  66 ,  68  on interior front and rear surfaces  60 ,  50  of the magazine body  12 . The follower guide rails  62 ,  64  have sufficient vertical length to prevent lateral tipping of the follower  18  as it travels along the length of the magazine body  12 . The forward follower guide rail  62  is shorter in vertical dimension than the rear follower guide rail  64  in the illustrated design to accommodate the curvature of the magazine body  12  and the position of a front magazine catch at the upper end  36  of the magazine  10 . 
         [0039]    As best illustrated in  FIGS. 4 and 8 , the upper surface  70  of the follower  18  may be, for example, divided laterally into a raised convex portion  72  and a lower concave portion  74 . The lower concave portion  74  cradles and guides a cartridge  44  against a lateral interior surface  46  of the magazine body  12 . In combination, the upper convex portion 72  of the follower  18  and an adjacent cartridge  44  guides another cartridge  44  against the opposing lateral interior surface  46 , maintaining portions of each cartridge rim in engagement with one of the rim guide channels  48  on each respective side. The height difference between the raised convex portion  72  and lower concave portion  74  maintains sequential cartridges  44  in a vertically staggered relationship, as well as their laterally staggered relationship. Other shapes for the upper surface of the follower  18  may be selected, as desired, in order to balance the resistance of both columns of cartridges  44 . 
         [0040]    As cartridges  44  are stripped away from the upper end  36  of the magazine  10 , cartridges  44  situated lower in the magazine  10  are moved from the double-stacked portion  42  into the transition portion  40 , where their relative vertical position increases as their relative lateral position decreases. This is best illustrated in  FIG. 4 . 
         [0041]    As cartridges  44  continue to be moved upwardly, through the transition portion  40 , they enter the upper or neck portion  38  of the magazine  10 , in which the cartridges  44  become vertically aligned in a single column with opposing edges of their rims both engaged in both opposing rim clearance channels  48 . In a preferred form, the vertical length of the neck portion  38  is kept to the minimum length necessary to engage the magazine well (not shown) of the selected shotgun, so that the combined transition portion  40  and double-stacked portion  42  of the magazine  10  may be maximized, thereby maximizing the capacity of the magazine  10 . 
         [0042]    Referring now in particular to  FIG. 9 , therein is shown an enlarged view of an upper portion of the magazine  10  seen in  FIG. 5 . The shotgun cartridges  44  are shown in phantom line in order to better view internal details of the magazine body  12  and are labeled individually as  44   a  through  44   d  for clarity of discussion. In or near the neck portion  38  of the magazine body  12 , the rim clearance channels  48  narrow toward the rear edge  50 . The forward edge  52  of the channel  48  ceases to be widely spaced from the rear edge  50  and presents an angled transition edge  76  which progressively decreases the width of the channel  48  toward a relatively narrowed rim guide channel  78 . The angled transition edge  76  and narrowed rim guide channel  78  are situated within or near the neck portion  38 , a region in which two opposite portions of cartridge rims  80  simultaneously engage both channels  48  on lateral interior walls of the magazine body  12 . 
         [0043]    As cartridges  44  are stripped from the upper end  36  of the magazine  10 , cartridges at a lower position, such as that shown as  44   c,  migrate upwardly. As the rim  80  is engaged on both lateral sides, it is drawn rearwardly by the angled transition edge  76  to a position generally represented by cartridge  44   b.  At this point, even if the rims  80  of the cartridges  44  are “misaligned” as shown by  44   b  and  44   c  in  FIG. 9 , each cartridge  44  is moved rearwardly until the rim  80  is positioned in the narrow rim guide channel  78 . As the cartridges  44  continue to progress upwardly, such as from the position of cartridge  44   b  to cartridge  44   a,  an upper portion of the rim  80  bears against a forwardly-sloped rear wall portion  82 . This movement reorients the uppermost cartridge  44   a  relative to the cartridge  44   b  below it, and forces the rim  80  into appropriate alignment as it passes a shoulder  84  at an upper end of the narrowed rim guide channel  78 . In this position, the rim  80  of the cartridge  44   a  is pressed against the feed lips  16  by spring pressure and is in position to be stripped away and chambered by the bolt of the firearm. 
         [0044]      FIG. 10  shows a cross-sectional view taken substantially along line  10 - 10  of  FIG. 6 . Therein can be seen the relative position of the narrowed rim guide channel  78  and lateral interior surfaces  46  of the magazine body  12  in the neck portion  38  of the magazine body  12  where the rim  80  of a cartridge  44  is engaged on both sides adjacent the rear wall of the magazine body  12 . 
         [0045]      FIGS. 11-13  show sequential pictorial views of the upper end  36  of the magazine  10  as cartridges  44  are sequentially moved upward. The rim  80  of each cartridge  44  is moved along and engaged by the rim guide channels  48  on opposite lateral interior walls of the magazine body  12 . As the rim  80  of each cartridge  44  encounters the angled transition edge  76 , the rim  80  is pulled rearward into the narrowed rim guide channel  78 . An upper edge of the cartridge rim  80  is guided by the forwardly-sloped rear wall portion  82  and pressed by spring force into position by the feed lips  16 . 
         [0046]    As used herein, “forward” or “front” refers to the muzzle or discharge end or direction of a firearm, distal from the user. “Rearward” or “rear” refers to end of the firearm proximal to the user and opposite the direction of a projectile discharge. “Up” or “upward” can, but does not necessarily, mean a vertically upward direction. Instead, these terms are meant to describe the direction of or movement toward the mouth or feed end of the magazine, even if a particular firearm utilizes a top or side loading magazine configuration or if the firearm may be mounted in different orientations. 
         [0047]    The illustrated embodiment was chosen and described to provide the best disclosure of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by any allowed claims when interpreted in accordance with the breadth to which they are fairly, legally and equitably entitled. The drawings and preferred embodiments do not and are not intended to limit the ordinary meaning of the claims and their fair and broad interpretation in any way.