Abstract:
An arcuate magazine for a firearm, such as a rifle or carbine, which has a keyway and follower assembly for delivering rounds of ammunition one at a time to the firing area of the firearm and which may be fabricated from a single piece of metal and have a smooth interior free of welds and rough spots. The invention also includes a method of making such a magazine which includes the steps of deep drawing and wiping the magazine body under substantial pressure using a progressive die having numerous stations.

Description:
PRIORITY CLAIM 
       [0001]    This application claims priority from U.S. Provisional Patent Application Ser. No. 60/922,104 filed 6 Apr. 2007, entitled METHOD TO DRAW AND FORM A CURVED FIREARM CARTRIDGE MAGAZINE BODY WITH A KEYWAY. 
     
    
     BACKGROUND AND SUMMARY OF THE INVENTION 
       [0002]    This invention relates to a cartridge magazine for a firearm and a method for making such a magazine, and is more particularly related to such a magazine and method wherein the magazine is arcuate in shape and has a body preferably formed from a single piece of metal. 
         [0003]    Such a magazine is used to contain ammunition, such as a series of cartridges, which are fed one at a time by spring means into a firing chamber of a weapon. The spring means maintains pressure on the ammunition to force each cartridge in to the firing chamber, and when spent to deliver the next round into firing position. 
         [0004]    An example of a firearm using a magazine is the M16 rifle or carbine, which has become a standard rifle in the United States weapons arsenal and in other western countries. There are several variations of the M16 weapon family, such as the M16/A1, A2, A3 and A4, which are the primary infantry rifles used by the U.S. military and 15 NATO countries since the early 1960s. These weapons use a magazine of the type disclosed in this application embodying the present invention. 
         [0005]    Preferably, such a magazine is arcuately shaped, and has a substantially rectangular cross section with parallel opposed longer sides defined by the height of the cartridge arranged between parallel opposed shorter sides defined by the width of the cartridge. One end of the magazine is closed with a removable base plate, and the other end is open to permit a cartridge in juxtaposition to the firing chamber of the weapon to be placed in firing position. Preferably, such a magazine is fabricated from steel rather than plastic or aluminum, as the magazine is subject to heat and substantial stress when it is used in the field. 
         [0006]    Usually, as in the case of the M16 carbine series, such a magazine is loaded with about 30 shells, weighting about 18 ounces when filled. Such a magazine must fit into the receiver lower, which is on lower side of the weapon, and, so as not to interfere with the operation of the weapon, the magazine is preferably curved toward the barrel relative to the point of insertion into the firing chamber. Preferably, the magazine has a keyway formed in one of its thinner sides to train and direct the cartridge in a proper firing position for entry into the firing chamber of the weapon. Conventionally, the magazine is formed by appropriately bending multiple pieces of metal and spot welding the pieces together. These operations were crucial, because breaking, bending or malformation of the welds or misalignment of the parts could cause the cartridges to become canted or in extreme cases to fall from the magazine, making the use of the weapon ineffective or dangerous in the field. Correct formation of the keyway is critical: a magazine with a misshaped keyway could make the magazine unuseable as the magazine could not be installed in the receiver lower. 
         [0007]    The prior art disclosed a number of magazine structures, such as 
         [0008]    Alzamora et al U.S. Pat. No. 7,117,626, which covers a feed lips gauge for a magazine; 
         [0009]    Ciener U.S. Pat. No. 5,461,811, which discloses a machined magazine body; 
         [0010]    Sniezak et al U.S. Pat. No. 5,438,783, which teaches a handgun magazine having a slidable butt plate; 
         [0011]    Baldus et al U.S. Pat. No. 4,862,619, which defines a cast or molded encircling element for a handgun magazine; 
         [0012]    Chesnut U.S. Pat. No. 4,586,281, for a magazine adapted for use with various styles of weapons. 
         [0013]    Farrar et al U.S. Pat. No. 4,514,922, which shows a magazine having a special latching mechanism; 
         [0014]    Weed U.S. Pat. No. 1,400,252, which illustrates a primitive releasing structure for a magazine. These references cover a long period of development of various magazines and features for magazines, but they do not teach the novel construction and methods for fabricating a magazine embodying the present invention which may be used without significant failures and which is most dependable in the field. Many references in the prior art deal with magazines for handguns, and these magazines are not typical of magazines for rifles or carbines, which are subject to great field stress and situations where the very life of the user depends upon the effectiveness of the weapon. 
         [0015]    Prior art studies of magazines for such rifles and carbines show significant failure rates of prior art magazines, sometimes as high as 50% or more, but studies of magazines embodying the present invention demonstrate almost no failures. 
         [0016]    The arcuate magazine device embodying the present invention is strong and fabricated from steel to withstand field stress and has a smooth keyway and interior permitting free travel of a round from the magazine to the firing chamber of the weapon. These features are accomplished by using fabrication means which eliminate wrinkles and rough surfaces in the magazine, as well as selecting welding points which do not interfere with movement of the shell by the magazine follower mechanism. 
         [0017]    In the disclosed method the magazine blank is deep drawn from high carbon steel, preferably having a Rockwell harness of 34-38 RC, so that the piece will not bend too easily, but not so hard as to make the material brittle. The magazine blank is designed so that only a single seam is necessary to form it, and so that the keyway is free of welds or wrinkling or similar encroachments. This fabrication requires a metal pressing operation which draws and forms the magazine including the keyway in a single operation, preferably using a 600 ton press (but a lesser press could possibly be used) with an upper pressure pad having a male form arbor, and top male form block and bottom female form block. The top male form arbor presses down on the magazine blank pinched between the upper pressure pad and the lower pressure pad with about 5500 lbs. PSI of pressure while the female form arbor resists the downward draw movement with about 9000 lbs. PSI and thereby forming the keyway and one of the short sides in the bridge of the magazine. Two lower pressure pads also serve as the curved surface across which the blank is formed as the blank is drawn down between the lower pressure pads. If inadequate pressure is applied, the keyway fails to form. If excess pressure is applied, the metal tears. 
         [0018]    Preferably, the male arbor has pilots for locating the watch holes in the curved side of the magazine blank. These pilot holes preferably perform the function of keeping the blank in place during the draw and form operation and the wiping operation. Preferably, the edges of the form opposed to the keyway are used to weld close the magazine body by means of one or more additive welds, but the position of the weld could be elsewhere, so long as it doesn&#39;t interfere with the keyway and it does not adversely cause wrinkles or rough surfaces on the interior of the magazine when formed. This draw and form operation creates a magazine body oriented in the shape of a “U”, with the keyway forming the base of the “U”. Ribs may be added to the body to remove any wrinkling of the interior of the magazine and these ribs also add strength to the magazine and support the shell as it moves through the magazine. During the wiping operation, an inner flap is formed and an outer flap is formed running substantially parallel to the keyway enclosing the magazine and in position for welding. 
         [0019]    A robotic welder may be used to make the weld on the edges of the blank remote from the keyway, and this weld must follow the curvature of the magazine. After the blank is fully formed and welded into a single piece, a spring and follower is inserted into the closed magazine, and the base plate is applied to close the lower edge of the magazine. 
       OBJECTS AND ADVANTAGES OF THE INVENTION 
       [0020]    It is the object of the invention to provide an arcuate magazine for a rifle or carbine of the character described. 
         [0021]    Another object is to provide an arcuate magazine which is fabricated in one piece. 
         [0022]    Another object is to provide a body for an arcuate magazine which is closed by additive welds. 
         [0023]    Another object is to provide an arcuate magazine for a weapon which may be heat treated with nitride or the like to provide a hardened finish. 
         [0024]    Another object is to provide an arcuate magazine which has a substantially smooth interior substantially free of wrinkles and rough surfaces, particularly in its keyway. 
         [0025]    Another object is to provide an arcuate magazine which is welded closed on an edge remote from its keyway. 
         [0026]    Another object is to provide a method for fabricating an arcuate magazine which is drawn and formed into a blank having a central keyway, sides depending from the keyway and edges remote from the keyway for welding the blank closed. 
         [0027]    Another object is to provide a method for fabricating a blank for an arcuate magazine having a keyway which is formed and drawn by means of high pressure applied to both sides of the blank. 
         [0028]    These and other objects and advantages will become more apparent as this description proceeds, taking in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0029]    In the drawings: 
           [0030]      FIG. 1  is a perspective view of a part of a M16 weapon having a magazine inserted, with parts broken away to show the interior firing zone. 
           [0031]      FIG. 2  is a sectional view of the magazine taken on line  2 - 2  of  FIG. 1  and showing the follower mechanism in the center of the magazine. 
           [0032]      FIG. 2A  is a detailed sectional view of the magazine which shows an alternative way for closing the magazine body by welding an edge for the short side opposed to the keyway over the lower edge of a long side. 
           [0033]      FIG. 3  is an elevation view of one short side of the magazine showing the watch or pilot holes. 
           [0034]      FIG. 4  is a sectional view of the magazine taken on line  4 - 4  of  FIG. 3 , showing rounds, the follower assembly, the spring, follower housing and ribs. 
           [0035]      FIG. 5  is an elevational view of one short side opposed to the keyway side shown in  FIG. 3 , showing the additive welds closing the magazine body. 
           [0036]      FIG. 6  is a schematic view illustrating the stamped blanks being drawn at the draw station.  FIG. 6A  is a magazine blank not yet drawn but punched from the sheet metal and then trimmed. 
           [0037]      FIG. 7  is a schematic view showing the forming of the drawn blanks. 
           [0038]      FIG. 7A  is a sectional view taken on line  7 A- 7 A, showing the forming of the keyway, taken through a pilot hole. 
           [0039]      FIG. 8  is a sectional view showing the cam press putting the ribs and wiping the edge section in the magazine body. 
           [0040]      FIG. 9  is a sectional view similar to  FIG. 8  showing the cam press putting the ribs and wiping the edge section on the other side of the magazine body. 
           [0041]      FIG. 10  is a schematic view showing the installation of the follower, spring and spring base into the magazine, and the installation of the base plate. 
           [0042]      FIG. 11  is a front view of the draw and form station with the die closed. 
           [0043]      FIG. 12  is a side view of the draw and form station with the die open. 
           [0044]      FIG. 13  is a front view of the wipe station with the die open. 
           [0045]      FIG. 14  is a side view of the wipe station with the die closed. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     (I) The Magazine 
       [0046]    With reference to  FIGS. 1-5 , a magazine  10  embodying the present invention is installed in a rifle or carbine weapon W, in position for a round of ammunition to enter the firing area C of the weapon. The ammunition is delivered to the firing area C by means of a spring loaded follower  11  which travels through the magazine  10  as each round is placed in firing position. 
         [0047]    The magazine  10  is secured in the weapon W in a receiver R and the magazine comprises spaced apart short walls  12  and  13 , bridged by space apart long walls  14  and  15 . One of the short walls  12  has arranged therein a keyway  16 , and the other short wall  13  comprised of edge sections  17  and  18  which overlap one another and are secured by welds. A plurality of ribs  19  and  20  are arranged opposed and in line with one another in the long walls  14  and  15 , and on set of aligned ribs  21  and  22  may be larger and deeper than the other sets of ribs. Within the interior of the walls  12 - 15 , the follower  11  is positioned with a head  23 , sides  24  and tail  25  slidably engaged in the keyway  16 . Preferably, the magazine body is formed in one piece and closed by the additive weld or welds. 
         [0048]    As shown in  FIGS. 3-5 , the magazine  10  has an arcuate shape  26  and on its short walls  12 ,  13  with side  12  having the keyway  16 . Keyway  16  has a series of watch or pilot holes  27  permitting a view of the cartridges within the magazine. At the end of the magazine  10  remote from the follower  11  the magazine is closed by a base or floor plate  28 . Within the interior of the magazine  10 , there is a spring  29  secured at one end to a spring base  30  which rests on the base plate  28  and at its other end to the follower  11  such that the follower is urged by the spring  29  to lift the cartridges toward to weapon firing position C. The additive welds  31  extend along the length of the short wall  13  but leave the interior of the short wall  12  free of flux and additive material. The interior of walls  12 - 15  and the keyway  16  are substantially smooth and substantially without rough spots so that ammunition rounds may be slidably moved by the follower  11  through the magazine  10  to the firing position C. Alternatively, as shown in  FIG. 2A , the short wall  13   a  may be lengthened and a long wall  14   a  may be shortened and stepped inward to permit the edge section  17   a  of the short wall  13   a  to be folded over the end of the long wall  14   a  and welded in place for closing the magazine  10 .  FIG. 4  shows the follower  11  partially retracted in magazine  10  with rounds of ammunition being pushed by the follower  11  toward the top of the magazine  10 . 
         [0049]    Preferably, after the magazine body is fully fabricated, it is heat treated with nitrides. This heat treatment hardens the surfaces of the metal. 
       (II) The Method of Making the Magazine 
       [0050]    With reference to  FIGS. 6-10 , in a rolled metal sheet  45 , a somewhat rectangular magazine blank  40  is formed in the metal sheet  45  by punching and removing a U-like piece of metal from the metal sheet  45 . Prior to the drawing station, pilot or watch holes  27  are formed in the sheet so that they run along the center line of the magazine blank  40  perpendicular to the path of travel of the metal sheet  45 . The center line from one edge of the metal sheet  45  across the magazine blank  40  including the section with the pilot or watch holes  27  to the other edge of the metal sheet  45  approximating a bridge  55 . The magazine blank  40  is connected to the metal sheet  45  by the bridge  55 . The pilot or watch holes  27  are in line with the bridge  55 . Each magazine blank  40  form has two long edges  50 ,  51  parallel to the bridge  55  and four short sides  60  roughly perpendicular to long sides  50 ,  51 . At the draw station, there is a male form arbor  70 . The male form arbor  70  is fitted with pilot pins  80 . The pilot pins  80  are set to correspond to the watch or pilot holes  27 . When the male form arbor  70  is pressed in a downward direction during the draw operation the pilot pins  80  go through the magazine blank  40  helping to hold the magazine blank  40  in proper position. During the drawing operation, each short side  60  is angularly bent upwardly. The magazine blank  40  is held in place by an upper pressure pad  90  and lower pressure pad  100 . The male form arbor  70  presses downwardly while the female form arbor  110  presses upwardly drawing and forming the magazine blank  40 . After the drawing and forming operation, the magazine blank  40  has a the keyway  16  with the watch or pilot holes  27  running up the middle of the keyway  16 . The remaining metal bridge  55  connects the magazine blank  40  to the sheet or strip of metal  45  at spans  52 ,  53 . 
         [0051]    As shown in  FIG. 8 , a first pair of short sides  60  are pressed between forming blocks  75 ,  76  so as to add ribs  19 ,  21  and to wipe over the interior flap  17 . As shown in  FIG. 9 , a second pair of short sides  60  magazine blank  40  is then pressed by another set for forming blocks  85 ,  86  so as to add ribs  20 ,  22  to the other side of the magazine blank  40  and to wipe over exterior flap  18 . The action of the press as shown in  FIGS. 8 and 9  is bending the long edges  50 ,  51  at about 90 degrees and forming the ribs  19 - 21  smooths wrinkles which may have been formed in the magazine blank  40  and puts the magazine blank in the final shape of magazine  10 . With reference to  FIG. 10 , the long side edges  50  and  51  are then welded from the exterior of the magazine blank  40  to close the magazine  10 . The follower  11  with its head  23 , sides  24 , spring  29 , tail  25 , spring base  30  are then fitted into the interior of the magazine  10 . Finally, base plate  28  is set in place adjacent to spring base  30  to prevent exit of follower  11  and to complete the formation of the magazine  10 . 
         [0052]    During the drawing and forming operation and the wiping operations, the magazine blank  40  attention is paid to prevent rough surfaces and to insure that the rounds will travel smoothly through the magazine  10 . 
         [0053]    The magazine  10  in the preferred embodiment is fabricated in a progressive die with a series of stations. Preferably, the operations are as follows:
       1. Pierce the pilot holes  27  into the magazine blank  40 . One would use pressure sufficient to hold the magazine blank  40  and to strip the magazine blank  40  off the punch, that pressure being known as stripping pressure.   2. Notch the center of the magazine blank  40  using stripping pressure.   3. Trim the ends of the magazine blank  40  using stripping pressure.   4. Draw and form the magazine blank  40  to create the long sides  50 ,  51  and the short sides  60  using about 5500 lbs. PSI from above and about 9000 lbs. PSI from below as further explained below.   5. Form the ribs  19 - 22  and side wipe the top edge of the magazine blank  40  using sufficient pressure to hold the magazine blank  40  flat and wiping the edges  50 ,  51  with minimum pressure of about 2000 lbs. PSI. The rib forming operation and wiping operation could be done separately.   6. Re-strike the magazine blank  40 . The re-strike sets the form in its finished geometry where male and female form blocks strike the long and short sides of magazine blank  40  into magazine  10 . Little pressure is required.   8. Cut off scrap material.
 
Wrinkling of the interior of the magazine  10  is also taken out during the formation of the ribs  19 - 22 , to assure that there are not rough spots within the magazine body.
       
 
         [0061]    The draw and form station used in the method is shown in  FIGS. 11-12 , using multiple nitrogen cylinders  130  on top and multiple nitrogen cylinders  140  on the bottom. The magazine blank  40  is placed the between the upper pressure pad  90  and the lower pressure pad  100  with the male form arbor  70  above and the female form arbor  110  below. At the moment of the pressing operation, the male form arbor  70  descends and pushes the female form arbor  110  into a pocket. It is the pocket that wipes the sides. The male form arbor is set in the die. When the die is closing, the upper pressure pad  90  exerts about 5500 lbs. PSI on bottom side form blocks  100 . The female form arbor  110  descends and resists that descent with about 9000 lbs. PSI. Different nitrogen cylinders may be used such that they achieve the required pressures. Pressure may be achieved by a number of means including spring pressure or urethane pressure. Attention should be paid to the travel distance of the cylinders given the needs of particular travel distances to do the draw and form operation to the magazine blank  40 . In the preferred embodiment, on top four Moeller HR2400-125 nitrogen cylinders are used to create about 5500 lbs. PSI and on bottom three Moeller HR1500-100 are used to create about 9000 lbs. PSI. As depicted in  FIGS. 13-14 , at the wiping station, the top nitrogen cylinders  150  are HR 2400-125 and the bottom nitrogen cylinders  160   a  are Moeller HR1000-100 and  160   b  Moeller HR300-100 to wipe long side edges  50  and  51 . When the die closes, the long side edges of  50  and  51  are formed over the two form arbors  200 . In  FIG. 14  the wiping station is shown with the die in the open position. The cam pushers  210  force the male form arbors toward the center of the die with the edges  50  and  51  formed over the male form arbors  200 , The pressure creating devices at this station in the preferred embodiment are cylinders that that achieve about 2000 lbs. PSI. Parts  170   a  and  170   b  are spacers. The magazine is held in the magazine holder  220 . 
         [0062]    While many changes and modifications can be made in the structure of the magazine and in the method of making it within the spirit of the invention, it is not intended that the invention should be limited to the exact structure and steps shown and described.