Patent Publication Number: US-2017370666-A1

Title: Shotgun ammunition conversion system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a Continuation of U.S. patent application Ser. No. 15/239,343, filed Aug. 17, 2016, entitled “SHOTGUN AMMUNITION CONVERSION SYSTEM,” which is a Continuation of U.S. patent application Ser. No. 14/823,941, filed Aug. 11, 2015, now issued as U.S. Pat. No. 9,441,895, entitled “SHOTGUN AMMUNITION CONVERSION SYSTEM,” which is a Continuation of U.S. patent application Ser. No. 14/196,428, filed Mar. 4, 2014, now issued as U.S. Pat. No. 9,103,612, entitled “SHOTGUN AMMUNITION CONVERSION SYSTEM,” which claims priority to U.S. Provisional Application Ser. No. 61/773,771 filed Mar. 6, 2013, and entitled “CONVERSION KITS” and to U.S. Provisional Application Ser. No. 61/774,528 filed Mar. 7, 2013, and entitled “CONVERSION KITS.” 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to firearms, and more particularly to a shotgun ammunition conversion system that converts a repeating shotgun into a repeating rifle capable of firing centerfire and rimfire cartridges. 
     BACKGROUND OF THE INVENTION 
     A shotgun is a firearm that uses the energy of a shotgun shell to fire a number of small spherical pellets called shot, or a solid projectile called a slug. One popular type of shotgun is the repeating pump-action shotgun. A conventional pump-action shotgun is one in which the handgrip or forend can be pumped back and forth in order to cycle the action to eject a spent round of ammunition and to chamber a fresh one. A pump-action shotgun is typically fed from a tubular magazine underneath the barrel, which also serves as a guide for the movable forend. The rounds are fed one by one into the action through a port in the receiver, where they are lifted by a lever called the shell lifter and are pushed forward into the chamber by the bolt. A pair of interrupters at the rear of the magazine holds the rounds in place to facilitate feeding of one shell at a time. 
     The forend is connected to the bolt by one or two bars (two bars are considered more reliable because they provide symmetric forces on the bolt and pump and reduce the chances of binding). The motion of the bolt back and forth in a tubular magazine model also operates the shell lifter, which lifts the shells from the level of the magazine to the level of the barrel. Modern pump shotgun designs have a safety feature called a trigger disconnector, which disconnects the trigger from the sear as the bolt moves back, so that the trigger must be released and pulled again to fire the shotgun after it closes. 
     After firing a round, the bolt is unlocked and the forend is free to move. The shooter pulls back on the forend to begin the operating cycle. The bolt unlocks and begins to move to the rear, which extracts and ejects the empty shell from the chamber, cocks the hammer, and begins to load the new shell. In a tubular magazine design, as the bolt moves rearwards, a single shell is released from the magazine and is pushed backwards to come to rest on the shell lifter. 
     As the forend reaches the rear and begins to move forward, the shell lifter lifts up the shell, lining it up with the barrel. As the bolt moves forward, the round slides into the chamber, and the final portion of the forend&#39;s travel locks the bolt into position. A pull of the trigger will fire the next round, where the cycle begins again. 
     A shotgun is generally a smoothbore firearm, which means that the inside of the barrel is not rifled. The shot pellets from a shotgun spread upon leaving the barrel, and the power of the burning charge is divided among the pellets, which means that the energy of any one ball of shot is fairly low. Shotguns are very popular for bird hunting. Shotguns can also be used for more general forms of hunting with slugs. Shotguns are often used with rifled barrels in locations where it is not lawful to hunt with a rifle. Typically, a sabot slug is used in these barrels for maximum accuracy and performance. However, the relatively low muzzle velocity of slug ammunition, and the blunt, poorly streamlined shape of typical slugs that causes them to lose velocity very rapidly compared to rifle bullets, limits the effectiveness of shotguns with many types of game. 
     Therefore, a need exists for a new and improved shotgun ammunition conversion system that converts a repeating shotgun into a repeating rifle capable of firing centerfire and rimfire cartridges. These larger caliber and higher-powered cartridges relative to shotgun shells enable shotgun users to hunt a wider variety of game while in the field without requiring the user to carry two separate guns. In this regard, the various embodiments of the present invention substantially fulfill at least some of these needs. In this respect, the shotgun ammunition conversion system according to the present invention substantially departs from the conventional concepts and designs of the prior art, and in doing so provides an apparatus primarily developed for the purpose of converting a repeating shotgun into a repeating rifle capable of firing centerfire and rimfire cartridges. 
     SUMMARY OF THE INVENTION 
     The present invention provides an improved shotgun ammunition conversion system, and overcomes the above-mentioned disadvantages and drawbacks of the prior art. As such, the general purpose of the present invention, which will be described subsequently in greater detail, is to provide an improved shotgun ammunition conversion system that has all the advantages of the prior art mentioned above. 
     To attain this, the preferred embodiment of the present invention essentially comprises a detachable magazine well having a sleeve defining a rectangular passage adapted to removably receive an ammunition magazine, a boss extending forward of the sleeve and at a level above at least a portion of the sleeve, the boss being adapted to be received in the rear aperture of the host shotgun&#39;s magazine tube, and a tang extending rearward of the sleeve and defining a tang aperture operable to receive a fastener associated with a shotgun frame to secure the magazine well to the shotgun with the sleeve proximate and aligned with the loading port when the boss is received in the rear aperture of the magazine tube. The boss may have a lower cylindrical surface portion operable to contact a lower portion of the magazine tube adjacent to the rear aperture. The boss may be a cylindrical body. There are, of course, additional features of the invention that will be described hereinafter and which will form the subject matter of the claims attached. 
     There has thus been outlined, rather broadly, the more important features of the invention in order that the detailed description thereof that follows may be better understood and in order that the present contribution to the art may be better appreciated. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a right side view of a prior art pump-action shotgun. 
         FIG. 2  is an enlarged cutaway view of the current embodiment of a shotgun ammunition conversion system constructed in accordance with the principles of the present invention installed in a receiver of the shotgun of  FIG. 1 . 
         FIG. 3  is a top isometric view of a current embodiment of a shell lifter adapter of the present invention attached to a shell lifter of the shotgun of  FIG. 1 . 
         FIG. 4  is an exploded view of the shell lifter adapter of  FIG. 3 . 
         FIG. 5  is a bottom isometric view of the shell lifter adapter of  FIG. 3 . 
         FIG. 6  is an enlarged cutaway right side view of a bolt, shoe, and barrel extension of the present invention installed in a receiver of the shotgun of  FIG. 1  in a first position. 
         FIG. 7  is an enlarged cutaway left side view of  FIG. 6 . 
         FIG. 8  is an enlarged cutaway right side view of a bolt, shoe, and barrel extension of the present invention installed in a receiver of the shotgun of  FIG. 1  in a second position forward of the first position of  FIG. 6 . 
         FIG. 9  is an enlarged cutaway left side view of  FIG. 8 . 
         FIG. 10  is a rear isometric partial view of a current embodiment of a magazine tube adapter of the present invention. 
         FIG. 11  is a top enlarged sectional view of the magazine tube adapter of  FIG. 11  with the forend of the shotgun of  FIG. 1  in the forwardmost position. 
         FIG. 12  is a top enlarged sectional view of the magazine tube adapter of  FIG. 11  with the forend of the shotgun of  FIG. 1  in the halfway retracted position. 
         FIG. 13  is a top partial sectional view of the magazine tube adapter of  FIG. 12 . 
         FIG. 14  is a top enlarged sectional view of the magazine tube adapter of  FIG. 11  with the forend of the shotgun of  FIG. 1  in the rearwardmost position with the rearmost cartridge partially pushed onto the shell lifter adapter of  FIG. 3 . 
         FIG. 15  is a top enlarged sectional view of the magazine tube adapter of  FIG. 11  with the forend of the shotgun of  FIG. 1  in the rearwardmost position with the rearmost cartridge fully pushed onto the shell lifter adapter of  FIG. 3 . 
         FIG. 16  is a top enlarged sectional view of the magazine tube adapter of  FIG. 11  with the forend of the shotgun of  FIG. 1  returned to the forwardmost position. 
         FIG. 17  is a rear isometric partial view of an alternative embodiment of a magazine tube adapter of the present invention. 
         FIG. 18  is a bottom enlarged sectional view of the magazine tube adapter of  FIG. 17  with the forend of the shotgun of  FIG. 1  in the forwardmost position. 
         FIG. 19  is a bottom enlarged sectional view of the magazine tube adapter of  FIG. 17  with the forend of the shotgun of  FIG. 1  in the rearwardmost position with the rearmost cartridge partially pushed onto the shell lifter adapter of  FIG. 3 . 
         FIG. 20  is a bottom enlarged sectional view of the magazine tube adapter of  FIG. 17  with the forend of the shotgun of  FIG. 1  in the rearwardmost position with the rearmost cartridge fully pushed onto the shell lifter adapter of  FIG. 3 . 
         FIG. 21  is a bottom enlarged sectional view of the magazine tube adapter of  FIG. 17  with the forend of the shotgun of  FIG. 1  returned to the forwardmost position. 
         FIG. 22  is a top isometric view of a current embodiment of the magazine adapter of the present invention. 
         FIG. 23  is a bottom isometric view of the magazine adapter of  FIG. 22  installed on the receiver of the shotgun of  FIG. 1 . 
         FIG. 24  is a right side sectional view of the magazine adapter of  FIG. 22  installed on the receiver of the shotgun of  FIG. 1 . 
         FIG. 25  is an enlarged sectional view taken along line  25  of  FIG. 24 . 
     
    
    
     The same reference numerals refer to the same parts throughout the various figures. 
     DESCRIPTION OF THE CURRENT EMBODIMENT 
     Embodiments of a shotgun conversion system of the present invention are shown and generally designated by the reference numerals  100 ,  200 ,  300 ,  400 ,  500 ,  600 , and  700 . 
       FIG. 1  illustrates a prior art shotgun  10  suitable for use with the present invention. More particularly, the shotgun is a conventional pump-action repeating shotgun such as the Model 870™ manufactured by Remington Arms Company, LLC of Madison, N.C. and the Mossberg® 500 and Mossberg® 590 manufactured by O.F. Mossberg &amp; Sons, Inc. of North Haven, Conn. The shotgun has a frame or receiver  12  having a top  14 , bottom  16 , front  18 , rear  20 , right side  22 , and left side  24  (shown in  FIG. 7 ). The right side of the receiver defines an ejection port  38 , and the bottom of the receiver defines a loading port  40 . The right side of the receiver defines two takedown pin apertures  42  that receive takedown pins  44  to releasably secure a trigger assembly  46  to the bottom of the receiver. A shell lifter  50  is pivotally attached to the front  48  of the trigger assembly by the forwardmost takedown pin  44 . 
     The receiver  12  has an interior  52  in communication with the ejection port  38 , loading port  40 , and the front  18 . The rear  56  of a bolt slide  54  is slidably inserted into the interior of the receiver through the front. A shoe  58  is attached to the rear of the bolt slide. A bolt assembly  80  including a bolt carrier  62  and a bolt  72  is attached to the shoe. The bottom  66  of the bolt carrier is attached to the top  60  of the shoe such that the front  64  of the bolt carrier faces towards the front of the receiver. The bolt carrier has a hollow interior  74  that receives the bolt. The rear  70  of a forend  68  is attached to the bolt slide in front of the bolt assembly. When the forend is pumped forward to chamber a round, the shoe slides forward and pushes a single locking lug upwards to place the bolt into battery. 
     The rear  28  of a magazine tube  26  and the rear  32  of a barrel  30  are connected to the front  18  of the receiver  12 . The barrel has a barrel ring  34  that slides over the magazine tube, indexes the barrel, and holds the barrel in place. A magazine tube spring with follower  36  is received within the magazine tube. The front  78  of a stock  76  is attached to the rear  20  of the receiver. 
       FIG. 2  illustrates a shell lifter adapter  100 , bolt assembly  200 , barrel  500 , and shoe  600  of the present invention. More particularly, the shell lifter adapter, bolt assembly, barrel, and shoe convert the repeating shotgun  10  into a repeating rifle capable of firing a rifle cartridge  80  instead of a 12 gauge shotgun shell. The cartridge has a front  84 , a rear  86 , and an exterior  88 . The shell lifter adapter  100 , bolt assembly  200 , and barrel  500  of the present invention can be adapted to chamber the shotgun to fire any suitable cartridge, including 0.50 BMG, 0.300 Win Mag, 0.308 Winchester, 7.62×39 mm, 5.56×45 mm NATO, and 0.22 LR, and preferably short action and lever action cartridges. The barrel, bolt assembly, and shoe of the current invention replace the barrel  30 , bolt assembly  80 , and shoe  58  of the shotgun  10 , and the shell lifter adapter attaches to the shell lifter  50 , without requiring any modification of the receiver  12 . 
     The rear  502  of the barrel  500  has threads  504  so that a barrel extension  506  can be threadably connected to the barrel. The barrel extension of the current invention has the same exterior dimensions as the barrel  30  of the shotgun  10  where the barrel extension is inserted into the front  18  of the receiver. The centerline of the barrel ring and the centerline of the barrel bore of the current invention will have the same dimension as the shotgun, but both the barrel and barrel ring of the current invention can have different external dimensions from the barrel  30  and barrel ring  34  of the shotgun. The interior surface  510  of the barrel extension defines barrel extension slots  508  that are sized to receive bolt lugs  208  on the exterior  210  of the bolt  206 . The front  210  of the bolt protrudes from the front  204  of the bolt carrier  202 . The bolt assembly  200  will be described in further detail in the discussion of  FIGS. 6-9 . 
       FIGS. 3-5  illustrate the shell lifter adapter  100  of the present invention. More particularly, the shell lifter adapter is shown removably attached to the shell lifter  50  of the shotgun  10 . The shell lifter  50  has a top  90 , bottom  92 , front  94 , and rear  96 . The front of the shell lifter has a U-shaped cutout  98 . A right tang  82  and a left tang  84  extend rearwardly. The right and has an aperture  86 , and the left tang has an aperture  88 . The apertures receive the forwardmost takedown pin  44  to pivotally attach the shell lifter to the trigger assembly  46 . 
     The shell lifter adapter  100  has a top  104  and a bottom  106 . The top of the shell lifter adapter defines a groove  108  that terminates in rear flanges  110  that are separated by a gap  112 . The gap permits the bolt lug to pass by, yet limits the rearward movement of the cartridge. The groove provides a cradle for the exterior  88  of the cartridge  80 . The rear flanges are positioned and shaped to permit the front  210  of the bolt  206  to pass over the top of the shell lifter adapter while still engaging the rear  86  of the cartridge to push the front  84  of the cartridge into the rear  502  of the barrel  500 . The top of the shell lifter adapter is shaped to lift the front or bullet end of the cartridge up so that when the bolt slides forward, the bullet end of the cartridge will feed smoothly into the chamber in the rear of the barrel. 
     As is shown in  FIGS. 4 and 5 , the shell lifter adapter  100  utilizes the existing U-shaped cutout  98  in the front  94  of the shell lifter  50  to removably attach to the shell lifter. The bottom  106  of the shell lifter adapter has a U-shaped snap/spring  120  that is adapted to closely fit the cutout in the shell lifter. An optional bottom shell lifter adapter  102  has a top  114 , a bottom  116 , and a U-shaped cutout  118 . The cutout in the bottom shell lifter adapter snaps over the portion of the snap/spring that protrudes from the cutout in the shell lifter. The front of the shell lifter is essentially clamped between the bottom  106  of the shell lifter adapter and the top of the bottom shell lifter adapter. 
       FIGS. 6 &amp; 7  illustrate the bolt  206  and shoe  600  of the present invention. More particularly, the bolt carrier  202  is not shown for clarity, and the bolt and shoe are shown in a first position where the rounded head  214  of a locking pin  212  has initially contacted the interior surface  510  of the barrel extension  506  as the forend  68  is moved forwardly. The bolt has a rear bore  220  and a forward bore  222 . The rear bore receives a cam pin  218  that has one end that protrudes downward from the rear bore and rides in a helical groove  604  in the top  602  of the shoe  600 . The cam pin can also ride in a similar groove in the bolt carrier. 
     The forward bore  222  receives a cam pin  214  that has one end with a semicircular groove  216  that protrudes downward from the forward bore. The semicircular groove engages a cylindrical locking pin  212  that is received laterally within a bore (not shown) in the bolt carrier. The locking pin has a milled recess or slot  224  (shown in  FIG. 8 ) that is located towards the middle of the locking pin. The slot is sufficiently wide enough to permit passage of the end of the cam pin  214  with the semicircular groove. In the first position, the engagement of the locking pin with the cam pin holds the bolt  206  forward within the bolt carrier. The engagement of the locking pin with the cam pin also keeps the bolt lugs  208  axially registered with the barrel extension slots  508  in the barrel extension  506  so the bolt lugs can pass through the barrel extension slots. 
       FIGS. 8 &amp; 9  illustrate the bolt  206  and shoe  600  of the present invention. More particularly, the bolt carrier  202  is not shown for clarity, and the bolt and shoe are shown in a second position that is forward of the first position described previously with the forend  68  in its forwardmost position. In the second position, the rounded head  214  of the locking pin  212  has been shifted laterally by contact with the interior surface  510  of the barrel extension  506 . The slot  224  in the locking pin has shifted laterally so that the slot is axially registered with the end of the cam pin  214  with the semicircular groove  216 . Disengagement of the semicircular groove from the locking pin has permitted the shoe  600  and locking pin to move forward relative to the cam pin  214  once the round is chambered and the bolt lugs  208  have passed through the barrel extension slots  508 . The continued forward movement of the shoe has caused the cam pin  218  to ride rearwardly in the helical groove  604 . As the cam pin rides rearwardly in the helical groove, the cam pin has been forced to rotate, which in turn has forced the bolt to rotate into battery. The rotation of the bolt has altered the relationship between the bolt lugs and the barrel extension slots so that the bolt lugs are no longer axially registered with the barrel extension slots. The bolt cannot move rearwardly until the forend is pulled rearwardly to rotate the bolt and realign the bolt lugs with the barrel extension slots. 
       FIG. 10  illustrates the magazine tube adapter  300  of the present invention. More particularly, the magazine tube adapter enables the magazine tube  26  of the shotgun  10  to accept cartridges  82  that are smaller than a shotgun shell. The magazine tube adapter has an outer diameter that is sized to be closely received within the magazine tube and a central bore  310 . At one end, the magazine tube adapter  300  defines a shoulder  312  that decreases the outer diameter of the magazine tube adapter. The decrease in the outer diameter of the magazine tube adapter at one end permits the installation of a collar  314  with a central bore  318  without enlarging the outer diameter of the magazine tube adapter at that end. The magazine tube adapter has slots (slot  306  is shown) at the top  302  and bottom  304 . The collar has slots  316  and  308  at the top  324  and bottom  326 . The slots in the magazine tube adapter and the collar are contiguous and enable the magazine tube adapter to be inserted into the magazine tube and clear the detents therein. The magazine tube adapter has a left slot  328  and a right slot  330  that are aligned with a left interrupter  320  and a right interrupter  322  formed in the collar. In the current embodiment, the left and right interrupters are generally shaped like a lowercase H, and the right interrupter has an inward protrusion  336 . The function of the left and right interrupters will be described subsequently in the description of  FIGS. 11-16 . In the current embodiment, the magazine tube adapter is made of plastic and the collar is made of spring steel. 
       FIGS. 11-16  illustrate the magazine tube adapter  300  of the present invention. More particularly, the interaction of the left and right interrupters  320 ,  322  formed in the collar  314  of the magazine tube adapter with the left magazine tube interrupter  332  and right magazine tube interrupter  334  in the receiver  12  of the shotgun  10  is shown. In  FIG. 11 , the forend  68  is in the forwardmost position. The rearmost cartridge  82  is retained within the central bore  310  of the magazine tube adapter by the left interrupter  320 . The left interrupter  320  is pulled inwardly by the left magazine tube interrupter  332 . 
     In  FIGS. 12 &amp; 13 , the forend  68  is half retracted. The rearmost cartridge  82  continues to be held in place by the left interrupter  320 . However, the right magazine tube interrupter  334  has begun to pull the right interrupter  322  inwardly. The rear  338  of the next cartridge  340  is shown abutting the front  84  of the rearmost cartridge  82 . 
     In  FIG. 14 , the forend  68  is fully retracted into the rearmost position. The left magazine tube interrupter  332  has pulled the left interrupter  320  outwardly, thereby disengaging the left interrupter from the rear  86  of the rearmost cartridge  82 . Disengagement of the left interrupter from the rear of the rearmost cartridge has permitted the magazine tube spring with follower  36  to begin to urge the rearmost cartridge rearward onto the shell lifter adapter  100  on the shell lifter  50 . The right magazine tube interrupter  334  has further pulled the right interrupter  322  inwardly so that the inward protrusion  336  on the right interrupter can engage with the rear  338  of the next cartridge  340  to retain the next cartridge within the magazine tube adapter  300 . 
     In  FIG. 15 , the forend  68  is still fully retracted into the rearmost position. The left magazine tube interrupter  332  has pulled the left interrupter  320  outwardly, thereby disengaging the left interrupter from the rear  86  of the rearmost cartridge  82 . Disengagement of the left interrupter from the rear of the rearmost cartridge has permitted the magazine tube spring with follower  36  to push the rearmost cartridge rearward fully out of the magazine tube adapter  300  and onto the shell lifter adapter  100  on the shell lifter  50 . The magazine tube spring with follower has also pushed the rear  338  of the next cartridge  340  into engagement with the inward protrusion  336  on the right interrupter  322 . 
     In  FIG. 16 , the forend  68  has returned to the forwardmost position depicted in  FIG. 11 . The right magazine tube interrupter  334  has pulled the right interrupter  322  outwardly to disengage the inward protrusion  336  on the right interrupter from the rear  338  of the next cartridge  340 . Simultaneously, the left magazine tube interrupter  332  has pulled the left interrupter  320  inwardly so the next cartridge  340  is retained within the central bore  310  of the magazine tube adapter by the left interrupter. As the interrupters move, the magazine tube spring with follower  36  urges the next cartridge rearwardly once the right interrupter has disengaged from the rear of the next cartridge. The cycle can then repeat. 
       FIG. 17  illustrates an alternative embodiment of the magazine tube adapter  700  of the present invention. More particularly, the magazine tube adapter enables the magazine tube  26  of the shotgun  10  to accept cartridges  82  that are smaller than a shotgun shell. The magazine tube adapter has an outer diameter that is sized to be closely received within the magazine tube and an asymmetrical bore  710  that is preferably shifted to the left of center so the left magazine tube interrupter  332  can directly engage the rearmost cartridge. However, the asymmetrical bore can also be shifted to the right of center so the right magazine tube interrupter  334  can directly engage the rearmost cartridge. At one end, the magazine tube adapter  700  defines a shoulder  712  that decreases the outer diameter of the magazine tube adapter. The decrease in the outer diameter of the magazine tube adapter at one end permits the installation of a collar  714  with a central bore  718  without enlarging the outer diameter of the magazine tube adapter at that end. The magazine tube adapter has slots (slot  706  is shown) at the bottom  702  and top  704 . The collar has slots  716  and  708  at the bottom  724  and top  726 . The slots in the magazine tube adapter and the collar are contiguous and enable the magazine tube adapter to be inserted into the magazine tube and clear the detents therein. The magazine tube adapter has a right slot  728  (shown in  FIG. 18 ) and a left slot  730  that are aligned with a right interrupter  720  and a left slot  722  formed in the collar. In the current embodiment, the right interrupter is generally shaped like a lowercase H and has an inward protrusion  736 . The function of the right interrupter and the left slot  722  will be described subsequently in the description of  FIGS. 18-21 . In the current embodiment, the magazine tube adapter is made of plastic and the collar is made of spring steel. 
       FIGS. 18-21  illustrate the alternative embodiment of the magazine tube adapter  700  of the present invention. More particularly, the interaction of the right interrupter  720  formed in the collar  714  of the magazine tube adapter with the right magazine tube interrupter  334  and left magazine tube interrupter  332  in the receiver  12  of the shotgun  10  is shown. In  FIG. 18 , the forend  68  is in the forwardmost position. The rearmost cartridge  82  is retained within the asymmetrical bore  710  of the magazine tube adapter by the right interrupter  720 . The right interrupter is pulled inwardly by the right magazine tube interrupter  334 . 
     In  FIG. 19 , the forend  68  is fully retracted into the rearmost position. The right magazine tube interrupter  334  has pulled the right interrupter  720  outwardly, thereby disengaging the right interrupter from the rear  86  of the rearmost cartridge  82 . Disengagement of the right interrupter from the rear of the rearmost cartridge has permitted the magazine tube spring with follower  36  to begin to urge the rearmost cartridge rearward onto the shell lifter adapter  100  on the shell lifter  50 . The left magazine tube interrupter  332  has moved inwardly through the left slot  722  so that the left magazine tube interrupter can engage with the rear  338  of the next cartridge  340  to retain the next cartridge within the magazine tube adapter  300 . The rear  338  of the next cartridge  340  is shown abutting the front  84  of the rearmost cartridge  82 . 
     In  FIG. 20 , the forend  68  is still fully retracted into the rearmost position. The right magazine tube interrupter  334  has pulled the right interrupter  720  outwardly, thereby disengaging the right interrupter from the rear  86  of the rearmost cartridge  82 . Disengagement of the right interrupter from the rear of the rearmost cartridge has permitted the magazine tube spring with follower  36  to push the rearmost cartridge rearward fully out of the magazine tube adapter  700  and onto the shell lifter adapter  100  on the shell lifter  50 . The magazine tube spring with follower has also pushed the rear  338  of the next cartridge  340  into engagement with the left magazine tube interrupter  332 . 
     In  FIG. 21 , the forend  68  has returned to the forwardmost position depicted in  FIG. 18 . The left magazine tube interrupter  332  has moved outwardly to disengage from the rear  338  of the next cartridge  340 . Simultaneously, the right magazine tube interrupter  334  has pulled the right interrupter  720  inwardly so the next cartridge  340  is retained within the asymmetrical bore  310  of the magazine tube adapter by the inward protrusion  736  on the right interrupter. As the interrupters move, the magazine tube spring with follower  36  urges the next cartridge rearwardly once the left interrupter has disengaged from the rear of the next cartridge. The cycle can then repeat. 
       FIGS. 22-25  illustrate the magazine adapter  400  of the present invention. More particularly, the magazine adapter enables the shotgun  10  to feed ammunition from a detachable box magazine  428  (shown in  FIG. 24 ) instead of the magazine tube  26 . The magazine adapter has a front  402 , rear  404 , and bottom  406 . The front has a sleeve  430  that defines a magazine well  412 . A cylindrical boss  410  extends forward of the sleeve at a level above at least a portion of the sleeve. The boss defines a horizontal axis  438  that is perpendicular to a vertical axis  440  defined by the sleeve. The boss extends forward of a left tang  414  and a right tang  416  that extend rearwardly from opposed side panels  436  that extend above the sleeve. The left tang has apertures  418 ,  420 , and the right tang has apertures  422 ,  424 . One side of the magazine adapter defines a magazine latch slot  408 . The magazine latch slot receives a magazine latch  426  that releasably secures the magazine within the magazine well. The magazine passes between the action bars (action bar  442  is shown in  FIG. 25 ) of the forend  68  when the magazine is received by the magazine well. In the current embodiment, the boss is made of plastic or aluminum, and the magazine well is rectangular. 
     The two opposed side panels  436  of the magazine adapter  400  that extend above the sleeve  430  are spaced apart to closely receive the bottom  16  portion of the receiver  12 . An upper surface portion  428  of the opposed side panels contacts the bottom of the receiver to enclose the loading port  40  with the magazine well  412  axially registered with the loading port. First, the shell lifter  50  is removed from the receiver or trigger group assembly. Subsequently, the boss  410  is inserted into the rear aperture of the magazine tube  26  to releasably retain the front of the magazine adapter via contact of a lower cylindrical surface portion with a lower portion of the magazine tube adjacent to the rear aperture. The cylindrical boss has a diameter sized to be closely received in the magazine tube. The left and right tangs  414 ,  416  are then positioned on the right and left sides  22 ,  24  of the receiver so that the apertures  418 ,  420 ,  422 ,  424  are axially registered with the takedown pin apertures  42 . The takedown pins  44  are replaced with longer cylindrical pins or threaded bolts (not shown) to removably secure the rear  404  of magazine adapter to the receiver. 
     In the configuration depicted in  FIG. 22-25 , the magazine adapter  400  enables 12 gauge shotgun shells to be fed from a detachable box magazine  428  into the shotgun  10 . However, it should also be appreciated that when the appropriate bolt assembly  200  and barrel  500  of the current invention are also installed, any suitable rifle cartridge can be fed from a suitable detachable box magazine into the shotgun  10 . 
     While current embodiments of a shotgun ammunition conversion system have been described in detail, it should be apparent that modifications and variations thereto are possible, all of which fall within the true spirit and scope of the invention. With respect to the above description then, it is to be realized that the optimum dimensional relationships for the parts of the invention, to include variations in size, materials, shape, form, function and manner of operation, assembly and use, are deemed readily apparent and obvious to one skilled in the art, and all equivalent relationships to those illustrated in the drawings and described in the specification are intended to be encompassed by the present invention. For example, the shotgun ammunition conversion system of the current invention works with any repeating action shotgun such as semi-automatic, automatic, and lever action, in addition to the pump action shotgun described. Furthermore, the cylindrical boss could be any suitable shape that fits the magazine tube, including hexagonal, octagonal, and semi-cylindrical. The critical surface is the bottom of the boss. Any shape that provides at least two points of contact in the lower half of the boss, to provide against the front end being lowered from its position or shifted laterally, is suitable. 
     Therefore, the foregoing is considered as illustrative only of the principles of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.