Abstract:
A firearm modification method and kit assembly includes the removal of the pistol style hand grip mount in a manner that precludes the use of the originally mounted pistol style hand grip, the modification of the hand grip mount to add a shoulder stock mount, and the installation of a shoulder stock in place of the originally mounted pistol style hand grip and hand grip mount.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 60/875,501, filed Dec. 19, 2006, which is incorporated herein by reference. 
     
    
     FIELD OF INVENTION 
       [0002]    The present invention relates to firearms in general and, more particularly, to a method for modifying a firearm to remove a pistol style hand grip mount in a manner that precludes the use of the originally mounted pistol style hand grip. The firearm is modified to add a shoulder stock mount and shoulder stock in place of the originally mounted pistol style hand grip and hand grip mount. 
       BACKGROUND OF THE INVENTION 
       [0003]    Many of the shoulder stocks mounted on semi-automatic firearms when purchased or available in the aftermarket have designs that constrain the mechanical operation of the firearm. The location and operation of reciprocating carrier and bolt, gas system, recoil system, barrel, magazine well, and firing mechanism sometimes dictate the placement of shoulder stocks and grips in less than ideal positions for the operator. For example the M-16/AR-15 family of firearms usually has a forward mounted gas system in which gas pressure drives a bolt carrier assembly aft to a recoil position and the bolt carrier assembly is then driven forward into battery position by a recoil spring and buffer mounted in a tube in the shoulder stock. The buffer recoil tube is positioned inside the shoulder stock in a direct line with the barrel and at the opposite side of the receiver. The designed position of the buffer tube in the stock prevents the shoulder stock from being lowered or moved into a normal rifle configuration that places the aft end of the stock lower than the receiver and squarely against the shoulder. The usual M-16 style stock does not sit comfortably or properly against the shooter&#39;s shoulder to allow for efficient absorption of recoil energy or for comfortable rifle handling. In an upright shooting stance up to half of the upper part of the stock butt pad is above and not in contact with the shooter&#39;s shoulder. The most efficient transfer of recoil energy is to spread it over as large an area as possible. The felt recoil from the 0.223/5.56 mm cartridge fired by an M-16 is not great, but with the M-16/AR-15 now being adapted for much more powerful ammunition, the handling of recoil energy becomes important to the shooter. What is needed is the ability of the shooter to place the shoulder end of the rifle stock more appropriately and comfortably against the operator&#39;s shoulder no matter what type of cartridge is fired. 
         [0004]    The stocks available for many gas operated firearms also place the shooter&#39;s sightline very high in relation to the barrel, causing sighting problems in some situations. In the example of M-16/AR-15 style of firearms, as seen in  FIG. 16 , the top of the shoulder stock is on a higher horizontal plane as compared to the top of the barrel. Because of the height of the stock, the shooter&#39;s head and eye line cannot get close to axis of the barrel. The sightline is typically raised to more than 2″ above the barrel centerline axis in such firearms. A high sightline causes more parallax than is efficient. This parallax is evident when the shooter shifts his point of aim from a close target to a distant one, or the reverse, causing the projectile&#39;s point of impact to change dramatically unless the sights are adjusted for change in distance. Parallax is not a problem for most target shooters, but for a hunter, an action competition shooter, or for a soldier, parallax can cause significant problems. The closer the sightline is to the barrel, the less the parallax and thus there is less of a shift in the point of impact between close and distant targets. What is needed is a method for enabling the sightline of an M-16/AR-15 style of firearm to be shifted closer to the barrel and for enabling a more vertical and thus more comfortable positioning of the shooter&#39;s head when acquiring the sightline. This is also the case when mounting optical, telescopic, holographic, or laser sights. 
       SUMMARY OF THE INVENTION 
       [0005]    According to the present invention, the shoulder end of the rifle stock is enabled to be placed more appropriately and comfortably against the operator&#39;s shoulder no matter what type of cartridge is fired. The present invention also positions the shoulder stock much lower in relation to the barrel, which thereby allows the shooter&#39;s sightline to be much lower and closer to the barrel resulting in less parallax. 
         [0006]    According to the present invention, the firearm is preferably modified by removing the shoulder stock, hand grip, and hand grip mount from the firearm, installing a modified shoulder stock mount where the hand grip mount was attached to the firearm, and mounting a modified shoulder stock to said modified shoulder stock mount. 
         [0007]    More specifically, according to the inventive method, sections from the top of the pistol grip mount are first measured and then removed. Next sections are measured and cut from metal, carbon fiber composites, or whatever the substance is appropriate for the firearm receiver. These pieces are then assembled to sandwich the remaining hand grip mount on the lower receiver just aft of the trigger and the trigger guard support. These pieces are preferably permanently attached by welding or bonding to form a new shoulder stock mount replacing the normal hand grip mount. A screw hole is preferably drilled and tapped through the back center of the new stock mount. A manufactured shoulder stock adapter may instead be made from appropriate matching materials and this adapter attached to the firearm receiver by bonding or welding. This adapter may be shaped to accept shoulder stocks made for other firearm mounts. The stock mount modification is substantial for its intended purpose and the mount is further braced by the trigger guard support and added fore and aft support is provided by the trigger guard being connected to the rigid magazine well. These modifications allow the mounting of a rifle style shoulder stock or butt stock in place of the originally mounted pistol style hand grip and stock. A rifle style shoulder stock, or butt stock for use according to the present invention is manufactured, modified, or adapted from wood, metal, plastics, composites, or other appropriate material, to fit the shape of the stock mount. A hole is then drilled the length of the stock and then a counter sink hole is drilled from the rear of the stock to allow for a 2-6″ screw to fasten the stock to the stock mount. The rear curve of the receiver is reshaped if more hand room is necessary above the stock for a comfortable hand rest. This rear curve modification may also remove the anti-rotation detent found in M-16/AR-15 style firearms, to preclude the secure mounting of the rifle&#39;s original style of shoulder stock in its normal position. 
         [0008]    In summary, the changes made to the original firearm&#39;s shoulder stock position and the removal of the pistol grip has a significant and positive effect on the operational handling and efficient use of the firearm. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a side view of an example of a known gas operated firearm. This example is in the family of the M-16/AR-15 with standard pistol style hand grip and stock which can be modified in accordance with the present invention. 
           [0010]      FIG. 2  is a side view of a gas piston operated firearm having a front mounted recoil system, which has been modified to have a rifle style shoulder stock mounted in accordance with the present invention in place of the pistol style hand grip and M-16 style stock. 
           [0011]      FIG. 3  is a side view of an alternative embodiment of a firearm having a standard gas impingement and short rear mounted recoil system, which has been modified in accordance with the present invention in a manner similar to the firearm shown in  FIG. 2 . 
           [0012]      FIG. 4  is a detailed partial side view of a prior art firearm showing a lower receiver with the hand grip mount and a pistol style hand grip dismounted. 
           [0013]      FIG. 5  is a detailed partial cross-sectional side view of a prior art firearm showing the mounted pistol grip with an assembly screw fixing the grip to the receiver. 
           [0014]      FIG. 6  is a detailed partial side view of a receiver showing the modified shoulder stock mount  55  according to the present invention for mounting the modified rifle style shoulder stock also shown. 
           [0015]      FIG. 7  is a detailed partial cross-sectional side view according to the present invention of a receiver showing the modified shoulder stock mounted on the modified stock mount with an assembly screw fixing the stock to the receiver. 
           [0016]      FIG. 8  is a rear view of a partially dismantled known gas operated firearm showing the position of the sight rail at the top, an M-16/AR-15 style stock mount in the middle, and a pistol style hand grip mount at the bottom. 
           [0017]      FIG. 9  is a rear view similar to  FIG. 8  with the addition of the pistol style hand grip mounted at the bottom. 
           [0018]      FIG. 10  is a rear view similar to  FIG. 9  with the addition of an M-16/AR-15 style shoulder stock mounted in the center. 
           [0019]      FIG. 11  is a rear detail view of a firearm receiver similar to one in  FIG. 8  which has been modified in accordance with the present invention to show a rifle style stock mount at the bottom in place of a pistol style hand grip mount. 
           [0020]      FIG. 12  is a rear view similar to  FIG. 11  with the installation of a rifle style shoulder stock to the rifle style stock mount shown in  FIG. 11 . 
           [0021]      FIG. 13  is a perspective close-up view of the bottom of a firearm receiver similar to the one represented in  FIGS. 2 ,  6 , and  11  modified in accordance with the present invention. 
           [0022]      FIG. 14  is a perspective close-up view of the receiver side of a rifle style shoulder stock similar to the one represented in  FIGS. 2 ,  6 , and  12  modified in accordance with the present invention. 
           [0023]      FIG. 15  is a side medium close-up view of the left side of a firearm receiver with stock attached similar to the one represented in  FIGS. 2 ,  7 , and  12  modified in accordance with the present invention. 
           [0024]      FIG. 16  is a full right side representation of standing person preparing to shoot a prior art M-16/AR-15 style firearm showing how the weapons shoulder stock contacts the shoulder. 
           [0025]      FIG. 17  is a full side view of a gas operated prior art M-16/AR-15 style firearm showing the sightline, distance of the sightline from the barrel and from the shoulder stock. 
           [0026]      FIG. 18  is a full side view of a firearm similar to one in  FIG. 13  which has been modified in accordance with the present invention. This illustration shows the sightline, distance of the sightline from the barrel and from the shoulder stock enabled by the modified shoulder stock. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0027]      FIG. 1  is a side view of an example of a known gas operated firearm  10 . This example is in the family of the M-16/AR-15 with standard pistol style hand grip and stock which can be modified in accordance with the present invention. As seen in  FIG. 1 , the firearm  10  has an upper receiver  45  with a barrel  40 , a fore end hand grip  21 , a front sight  41 , and a rear sight  43  mounted on a sight/scope rail  45  on top of the upper receiver  45 . The lower receiver  23 , is shown with a trigger guard  53 , a trigger guard support  56 , a pistol style hand grip  14 , and a shoulder stock  15 . 
         [0028]      FIG. 2  is a side view of a gas piston operated firearm  12  having a front mounted recoil system, which has been modified to have a rifle style shoulder stock mounted in accordance with the present invention in place of the pistol style hand grip and M-16 style stock.  FIG. 3  is a side view of an alternative embodiment of a firearm  13  having a standard gas impingement and short rear mounted recoil system, which has been modified in accordance with the present invention in a manner similar to the firearm shown in  FIG. 2 . 
         [0029]    Referring to  FIGS. 2 and 3 , the two firearms  12  and  13  share many of the same parts and functional characteristics with the firearm  10  in  FIG. 1 . Most of the parts on these three firearms are interchangeable except that the shoulder stocks  16  from the firearms shown in  FIGS. 2 and 3  would not fit on the lower receiver  23  in  FIG. 1 . The shoulder stock  15  and hand grip  14  from  FIG. 1  would not mount on the lower receivers  24  in  FIGS. 2 and 3 . Any of the upper receiver assemblies  45  with barrels  40 , fore ends  20  &amp;  21  and recoil groups  31  and  33  from  FIG. 2  or  32   a  from  FIG. 3  may be interchanged with any of the other firearm&#39;s lower receivers  23  &amp;  24 . The difference between the firearm  10  in  FIG. 1  and those in  FIGS. 2 and 3  is the modification in accordance with the invention that is represented primarily in  FIGS. 2 and 3  by the rifle style shoulder stocks  16  and the re-cut rear vertical curve  26  in lower receivers  24 . 
         [0030]    Referring now to  FIGS. 4 and 5 , a pistol style hand grip  14  in  FIG. 5  is shown attached to the lower receiver  23  similar to the one in  FIG. 1 . The hand grip  14  is typically held in place by a ¼″-28 tpi fastener  54  on the grip mount  51 .  FIG. 4  shows the pistol grip detached from grip mount  51 . The grip mount  51  is approximately a ¼″ thick and spans between the rear vertical curve  25  of the lower receiver  23  and the trigger guard support  56  just behind the trigger  52 . 
         [0031]      FIG. 6  is a detailed partial side view of a receiver showing the modified shoulder stock mount  55  according to the present invention for mounting the modified rifle style shoulder stock also shown.  FIG. 7  is a detailed partial cross-sectional side view according to the present invention of a receiver showing the modified shoulder stock mounted on the modified stock mount with an assembly screw fixing the stock to the receiver. 
         [0032]    Referring to  FIGS. 6 and 7 , a rifle style shoulder stock  16  in  FIG. 7  is shown attached to a lower receiver  24  similar to the ones in shown in  FIGS. 2 and 3 . The modified shoulder stock of the invention  16  is preferably fastened to the stock mount  55  of the invention by a ¼″-28 tpi fastener  57 .  FIG. 6  shows the shoulder stock detached from stock mount  55 . The stock mount  55  as seen in  FIG. 6  is preferably approximately ⅞″ thick side to side, 1¼″ tall, and ⅞″ front to rear, including the solid part of the trigger guard support  56 . The shoulder stock mount  55  of the invention is preferably permanently attached to bottom of the receiver body  24  just behind, and also permanently attached to, the rear of the trigger guard support  56 . These pieces are preferably permanently attached by welding or bonding to form the new shoulder stock mount  55 . 
         [0033]      FIG. 8  is a rear view of a partially dismantled known gas operated firearm  10  showing the position of the sight rail at the top, an M-16/AR-15 style stock mount in the middle, and a pistol style hand grip mount at the bottom.  FIG. 9  is a rear view similar to  FIG. 8  with the addition of the pistol style hand grip mounted at the bottom of firearm  10 .  FIG. 10  is a rear view similar to  FIG. 9  with the addition of an M-16/AR-15 style shoulder stock mounted in the center of the firearm  10 . 
         [0034]      FIGS. 8 ,  9 , and  10  show a rear view of a lower firearm receiver  23  of the prior art M-16/AR-15 family of firearms as shown at  10  in  FIG. 1 . The lower part of  FIG. 8  shows the pistol style grip mount  51  with the trigger guard support  58  showing on either side and the mounting screw hole  54  visible in between. In  FIG. 9 , the shoulder stock mount  27  is shown just above the stock anti-rotation detent  28 . At the top of these figures is the sight/scope rail  45 .  FIG. 9  is similar to  FIG. 8  with the addition of the mounted pistol grip  14 .  FIG. 10  is similar to  FIG. 9  with the further addition of the shoulder stock  15 . 
         [0035]      FIGS. 11 and 12  show a firearm receiver  24  similar to the receiver  23  shown in  FIGS. 8-10  except that it has features modified in accordance with the present invention. The lower receiver  24  in  FIG. 11  shows the shoulder stock mount  55  of the invention and also shows the mounting screw hole  57   a . Just above the mount is the rear vertical area  26  where material is preferably removed to provide a more comfortable hand placement. The removal of material from the rear vertical area of the receiver also removes the anti-rotational detent  28  of the original M-16/AR-15 stock mount  27 .  FIG. 12  has the same basic features as  FIG. 11  with the addition of a rifle style shoulder stock  16  modified in accordance with the invention. 
         [0036]      FIG. 13  is a view of shoulder stock mount  55  of the invention shown in an inverted perspective view. The shoulder stock mount  55  is seen in the center and in the center of the mount facing the viewer is the threaded screw hole that accepts a screw through the stock to fasten the stock to the mount. 
         [0037]      FIG. 14  is a perspective view of the modified rifle style shoulder stock  16  of the invention. At the bottom of the figure is the shaped notch and top side  55   a  that mates with the stock mount  55  on the receiver. This stock  16  is joined to the corresponding receiver mount  55  by the shown ¼″ screw  57  that fits into the matching threaded hole  57   a  in  FIG. 13 . 
         [0038]      FIG. 15  is a side view of a firearm receiver similar to the one in  FIGS. 2 and 13 . In this photo the modified shoulder stock  16  of the invention is mated with the receiver stock mount  55  of the invention. This mated configuration may also be seen in  FIGS. 2 ,  7 , and  12 . 
         [0039]    The full side view of  FIG. 16  is a representation of a man preparing to fire a prior art firearm in the M-16/AR-15 family. This figure demonstrates how the original M-16 style stock  15  sits high on the shooter&#39;s shoulder  11  in a common shooting stance. The stock  15  cannot be moved lower on the firearm because the recoil system tube  32  of the firearm extends into the top of the shoulder stock in the manner shown. 
         [0040]      FIG. 17  shows an M-16/AR-15 style firearm similar to the one in  FIG. 16 . The placement of the recoil tube  32  at the top of the stock  15  sets the placement of the stock high on the firearm. The sights  43  and  41  are positioned as low as they can be on the weapon to still allow the shooter enough room between the stock  15  and the sights to get his sighting eye in position for a sightline  49 . The relationship between the sightline  49  and the stock  15  is indicated at  48 , as well as the distance between the barrel  40  and the sightline  49  for comparison to what is shown in  FIG. 18 . 
         [0041]    A firearm modified according to the present invention is shown in  FIG. 18 . This illustration shows the sightline, distance of the sightline from the barrel and from the shoulder stock that is enabled by the modified shoulder stock according to the invention. As can be seen, the sightline  49  is closer to the barrel  40  than the sightline in  FIG. 17  by comparing distance  47  on both firearms.  FIG. 18  also shows the greater sightline  49  to shoulder stock  16  distances in comparison to same measured points in  FIG. 17 . The shooter&#39;s ability to get his head and sighting eye close to the sight rail is highlighted by comparing the positions of the shoulder stocks  15  and  16 , respectively, in  FIGS. 10 and 12 . Note the difference in the distance between the top of the stock  15  to the sight rail  45  in  FIG. 10  compared to the distance between the top of the stock  16  and the sight rail  45  in  FIG. 12 . 
         [0042]    It should be understood that the foregoing description is only illustrative of the invention. Various alternatives and modifications can be devised by those skilled in the art without departing from the invention. In addition, many suitable sizes and shapes or type of elements or materials could be used. Accordingly, the present invention is intended to embrace all such alternatives, modifications and variances which fall within the scope of the invention as claimed.