US3280495A

US3280495A - Revolver type firearm with interchangeable barrels and cylinders

Info

Publication number: US3280495A
Application number: US512363A
Authority: US
Inventors: Karl R Lewis
Original assignee: Individual
Current assignee: Individual
Priority date: 1960-11-23
Filing date: 1965-12-08
Publication date: 1966-10-25
Anticipated expiration: 1983-10-25
Also published as: US3221433A; US3303594A

Description

Oct. 25, 1966 R LEWIS 3,280,495

K. REVOLVER TYPE FIREARM WITH INTERCHANGEABLE BARRELS AND CYLINDERS Orlgnal Filed Nov. 23. 1960 F' l@ I /08 'lh 'nl /oo 'f g- F IG 2 2 /08 llo /8 50 54 40 /0 /4 /50 INVENTOF? KARI- R.. LEWIS ATTORNEYS United States Patent 3,289,495 REVOLVER TYPE FREARM WETH NTER- CHANGEABLE BARRELS AND CYLil DERS Karl R. Lewis, 77 Glney Rond, Wethersfield, Conn. Application Nov. i6, 1964, Ser. No. 411,470, which is a division of appiication Ser. No. 71,339, Nov. 23, 196i), new Patent No. 3,163,951, dated Jan. 5, 1965. Divided and this application Dec. 8, 1965, Ser. No. 512,363

4 Claims. (Cl. 42-59) This application is a division of my co-pending application, Serial No. 411,470, filed November 16, 1964, now abandoned, for Firearm Barrel, Frame and Cylinder Construction. This latter application is in turn a division of my previous application, Serial No. 71,339, filed November 23, 1960, for Firearm Firing Mechanism, now Patent No. 3,163,951.

This invention reiates to firearms, and deals more particularly with improvements in the construction of small firearms of the revolver type.

The general object of this invention is to provide a revolver-type firearm which is readily and easily converted from a Construction adapted for firing one size of cartridge to a construction adapted for firing another size cartridge.

A more particular object of this invention is to provide a. firearm of the foregoing character including interchangeable barrels and cylinders for the purpose of varying the size of cartridge fired by the firearm, the barrels, cylinders and other parts of the lirearm being so constructed as to make impossible a dangerous mismatch of a small caliber barrel with a large caliber cylinder.

Gther objects and advantages or the invention will be apparent from the following description and from the drawing forming a part hereof.

The drawing shows a preferred embodiment of the invention and such embodiment will be described, but it will be understood that various changes may be made from the construction disclosed, and that the drawing and description are not to be construed as deiining or limiting the scope of the invention, the claims forming a part of this specification being relied upon for that purpose.

Of the drawing:

FIG. l is a side view of a firearm embodying the present invention; and

FIG. 2 is a side View of the firearm shown in FIG. l with the upper portion thereof being shown in vertical longitudinal section and with the lower portion being shown in elevation with the grip pieces removed from the frame.

Referring now to the drawing, there is shown a iirearm embodying the invention and of the revolver pistol type. The iirearm comprises a frame which is provided with a mechanism cavity 12, a cylinder recess 14 and a crane recess 16 in the upper portion thereof. Between the mechanism cavity 12 and the cylinder recess 14 is a transverse or intermediate wall 18, and a longitudinal bore 2@ extends between the crane recess 16 and the mechanism cavity 12. The mechanism cavity l2 has one side wall 22 which is integral with the other portions of the frame. The outer surface of this wall is shown facing the viewer in FiG. 1. The other side wall of the mechanism cavity is provided by a removable side plate, not shown, which is attached to the side of the frame facing the viewer in FIG. 2 by means of screws or other fasteners. Removal of the side plate provides access to all of the parts of the firing mechanism shown in FlG. 2.

The lower portion of the frame includes a trigger guard 24 of conventional configuration and a depending grip S Patented Get. 25, 1966 portion 26 located rearwardly of the trigger guard. As shown in FIG. l, the grip portion of the frame comprises two generally downwardly extending

arms

28, 28 that are spaced apart longitudinally of the frame. The

arms

28, 28 have attached thereto, two vside pieces, one of which is shown at 30 in FIG. l, which are located one on either Side of the frame and which are preferably made of wood or plastic. These side pieces, together with the grip portion of the frame, constitute the grip of the firearm, the grip being hollow to provide a storage chamber for holding extra cartridges or other articles. Access to the storage chamber is provided by a pivotal lioor plate 32, as shown in FIG. 2, which is pivotally connected adjacent its rear end to the grip portion 26 and which at its forward end is provided with a releasable latch 34. The latch 34 normally holds the oor plate in closed position with respect to the storage chamber and is manually operable by a thumb or finger to release the ioor plate for swinging movement away from the grip portion.

A crane 36 is attached to the frame 1t) for outward swinging movement about an axis extending longitudinally of the frame. This mounting of the crane to the frame is obtained by providing the crane with a pivotal portion 38 which is loosely received by the longitudinal frame bore 26. As viewed in FIG. 1, the crane 36 is swingable outwardly about the axis of the longitudinal bore 2G in a direction toward the viewer from the position shown. Swinging movement of the crane in a direction away from the viewer in FIG. 1 is limited by engagement of the crane with the side wall of the crane recess. This side wall is not shown in FIG. l, but is located immediately behind the crane and is integral with the frame.

A cylinder 40 of somewhat conventional construction is rotatably secured to the crane for rotation about an axis extending longitudinally of the firearm. Normally, the cylinder 40 is positioned within the cylinder recess 14 as shown in FIGS. 1 and 2, but it is swingable outwardly therefrom with the crane 36 in order to displace the cylinder to an open position located to one Side of the frame for loading and ejecting purposes. The cylinder 49 includes a plurality of cartridge receiving chambers 42, 42 which are shown empty in FIG. 2. When the cylinder is in its normal position, the intermediate wall 18 of the frame and the flanges 44, 44, one of which is formed on either side of the frame behind the cylinder, at least partially close the rear ends of the cartridge chambers 42, 42 to prevent the addition or removal of cartridges to or from the chambers; however, when the cylinder is swung outwardly from the frame, the rear ends of the cylinder cartridge chambers are positioned away from the wall 18 and the adjacent ange 44 so that cartridges may be removed or added.

The cylinder 49 is rotatably secured to the crane 36 for rotation about an axis extending longitudinally of the frame. As shown in FIG. 2, the cylinder mounting means includes a sleeve 46 which is fixed to the crane 36 and extends rearwardly therefrom through the center of the cylinder 4t). The outer surface of the sleeve 46 fits loosely with the center bore of the cylinder 4i? to permit the cylinder to rotate about the sleeve. An ejector rod 4S is received within the sleeve 46 and is longitudinally slidable relative thereto, the sleeve 46 at its forward end having a reduced diameter section which engages and slidably supports the ejector rod. At its rear end, the ejector rod 4S is provided with a conventional cartridge extractor 5d which is movable rearwardly to eject the cartridges from the cylinder when the cylinder is disposed in its open position to the side of the frame. In ejecting the cartridges, the ejector engages the rims of the cartridges in the cartridge chamber and moves them rearwardly and out of the chambers. The ejector rod 43, it will be noted, extends fonwardly beyond the crane 36 and this forwardly extending portion of the rod is movable rearwardly by the user to effect a rearward cartridge eje-cting movement of the cartridge extractor. The ejector rod 4S and the cartridge extractor are normally held in the forward positions shown in FIG. 2 by a compression spring 52 which is located in the bore of the sleeve 46 and which at one end engages an abutment S4 in the cylinder 40 and on its other end engage-s an ejector rod collar 56 carried by the ejector rod 48.

The cylinder 4t) is normally held in the closed position illustrated in FIGS. l and 2 by means of a cylinder bolt 58 `which has a rearward portion slidably received in the lbore 6@ of the cartridge extractor and in the bore of a sleeve 62 fitted into the intermediate frame wall 18, and a forward portion slidably received in the bore 64 of lthe ejector rod 48. The cylinder bolt 58, as shown in FIG. 2, includes an integral collar 66 which is normally held in the rearward position shown by a spring 68. A means provided for moving the cylinder bolt 58 forwardly to unlock the cylinder from the frame for outward swinging movement thereof comprises a cam element 70 that is pivotally connected to the frame 10 for pivotal movement about a transverse axis between active and inactive positions. Ori its periphery, the cam element 7i? has two closely spaced

faces

72, 72 and two widely spaced

faces

74, 74. In its inactive position, the cam element 70 is positioned as shown in FIG. 2 so that one of the closely spaced faces 72 faces the hammer 76 while Ithe other face 72 engages a cylinder bolt release member 78 which has its forward part positioned in the sleeve 62 and in engagement with the rear end of the cylinder bolt 58, the cylinder bolt 58 under the action of its bias -urging the cylinder bolt release mem-ber 73 rearwardly and into engagement with the carn element 70. As shown in FIG. 2, the hammer 76 is engageable with the firing pin 80 when the cam element 7) is in the inactive position shown. The cam element 70 is moved to an active position by rotating it approximately 90 about its transverse axis from the position shown in FIG. 2. This brings one of the widely spaced faces 74 into opposing relation with the hammer 76 and causes the other face 74 to hold the cylinder bolt release member 7S in a forward position at which the cylinder bolt 58 is held out of the sleeve 62 so that the cylinder is freed for lateral swinging movement. The spacing of the

faces

74, 74 is such that the face which opposes the hammer 76 is engageable with the latter to hold it slightly rearwardly from its neutral position and to thereby prevent or block it from engaging the firing pin 80. The cam element '70 therefore in addition to serving as a part of the releasing mechanism for the cylinder also serves as a safety device for the rearm. Movement of the cam element 70 from its active to its inactive position, is produced by manual operation of a lever 82 located on the outside surface of the rearm as shown in FIG. 1, the latter being connected with the cam element 7G which extends through the side wall 22 of the mechanism cavity 12. With the lever 82 in the position marked F as shown in FIG. l, the cam element 70 is disposed in its inactive position so as to permit the hammer to engage the firing pin to cause firing of a cartridge, while with the lever in the position marked S in FIG. 1, as shown -by the broken lines, the cam 70 is in its active or safety position at which position the hammer is blocked against firing engagement with the pin and at which the cylinder bolt is released from the frame to permit lateral outward movement of the cylinder. At both the S and F positions of the lever 82 the frame 10 is provided with an indent, such as shown at 84 in FIG. 1, which cooperates with the lever to releasably hold it in the position to which it is moved.

Referring to FIG. l, it will also be noted that the llange 44 located on the side of the frame from which the cylinder 40 swings is provided with a cam surface 86 which engages the rear end of the cylinder bolt S and cams the same forwardly as the cylinder is swung from its open position back to its normal closed position. When the Cylinder is in its open position, it is held in place on the sleeve 46 by a blocking element 88 which is connected with the frame and has a forwardly facing surface that abuts the rear face of the cylinder to restrain its rearward movement.

The cylinder 40 is releasably held in a fixed angular position with respect to the frame 'by a cylinder stop 90 having a head 92 which is engagea-ble `with any one of

several cylinder notches

94, 94 which are formed in the outer surface of the cylinder and arranged in an annular series. The number of

notches

94, 94 corresponds to the number of cartridge chambers 42, 42 and the notches are so located that when the cylinder stop 92 is in locking engagement with a notch 94, a corresponding cartridge chamber 42 will be in proper operative relationship with the firing pin which is located in the intermediate wall 18.

The barrel 96 of the rearm is located in front of the cylinder 4t) and has a threaded rear portion 93 which is received in a corresponding threaded opening in the frame 10. The barrel, of course, is so located with respect to the frame and the cylinder 46 that the longitudinal axis of its bore is in alignment with the longitudinal axis of the upper or active chamber 42 which is held in firing position by the cylinder stop head 92. The forward end of the barrel 96 is provided with a radially outwardly extending flange 100. A shroud 102 surrounds the barrel 96 and extends substantially the entire length of the barrel from the forward end face of the frame to the barrel flange 103. The shroud 102 has a bore 104 for receiving the barrel which bore conforms closely to the outside surface of the barrel, but with a sufficiently loose t existing between the barrel and the shroud as to permit the barrel to slide longitudinally and angularly of the shroud during assembly or disassembly of the firearm. The shroud 102 is held longitudinally in place on the barrel by means of engagement with the forward face of the frame 10 at its rear end and `by means of engagement with the barrel flange 11N) at its other end. Angular displacement of the shroud with respect to the frame is prevented by means of a locking pin 106 which extends between the frame and the shroud and which is preferably located below the 'barrel as shown in FIG. 2. In FIG. 2, .the partial section illustrating the locking pin 106 is taken on a plane located in front of or closer to the viewer than the plane on which the remainder of the view is taken. The upper front portion of .the shroud 102 is provided with a front sight 108 which is preferably formed integral with the shroud, and a rear sight 110 is attached .to the rear portion of the frame 10 as shown in FIGS. 1 and 2.

As best shown in FIGS. 1 and 2, the shroud 102 also includes a longitudinally extending recess 112 formed in one side thereof for receiving the ejector rod 48 when the crane 36 and the cylinder 40 are in their normal closed or -ring positions with respect to the frame. Adjacent the forward end of the recess the shroud is provided with a bore 114, FIG. 2, which receives a spring 116 and a ball 118, the spring urging the ball rearwardly as shown and the -ball being retained lin the bore by the shroud being staked adjacent the mouth of the bore. The ball 118 extends partially from the bore 114 and normally engages the forward end -of the eject-or rod 48, the mouth of the bore 64 of the ejector rod forming a detent for receiving the ball. The spring loaded ball 118 therefore serves as a support for the forward end of the ejector rod when the cylinder is in closed or ring position.

The tiring mechanism of the tiring arm is located in the mechanism cavity 12 and is described in detail in my above-referred to patent to which reference is made for a more detailed description thereof. For the present, it is sufficient to note that in addition to the hammer 76 the mechanism includesv a trigger 120 which is supported for pivotal movement relative to the frame 10 by a pivot pin 122. The trigger 120 is movable in a conventional manner between forward and rearward positions relative to the frame and connected with the hammer is a means, indicated generally at 124 for controlling the movement of the hammer in response to the movement of the trigger. The trigger is biased in the counterclockwise direction, as viewed in FIG. 2, so that the lower portion thereof is normally held in the forward position illustrated. This bias for the trigger is provided by a connecting pin 126 which is pivotally connected to the upper portion of the trigger 120 `and which extends forwardly into a bore 128 formed in the pivotal portion 38 of the crane 36, there being provided in the bore 128 a helical compression spring 130 and a spring guide 132 which serve to engage the forward end of the connecting pin 126 and to urge it rearwardly. The spring guide 132 is slidably received in the bore 128 and extends forwardly through the center lof the spring 130 to prevent the spring from buckling or bending in the transverse direction. The rear end of the spring guide 132 is provided with an enlarged head having a forward face which abuts the spring 130 and a rear face which abuts the connector pin 125, the latter face preferably being provided with a depression for receiving the forward end of the connector, as illustrated. The spring 130 and the connector pin therefore function tc normally hold the lower portion 0f the trigger in the illustrated forward position and to oppose its movement to the rear.

In accordance with this invention, the firearm as illustrated lis so designed that both the barrel 96 and the Icylinder 40 may be replaced with other barrels and cylinders to adapt the rearm for use with cartridges of different calibers. As mentioned previously, and as shown in FIG. 2, the barrel 96 has a threaded rear portion 98 whi-ch is received in a corresponding threaded bore formed in the frame forwardly of the cylinder recess 14. Also, the shroud 102 which surrounds the barrel 95 has a loose t therewith so that the barrel may slide angularly and longitudinally relative to the shroud during assembly and disassembly of the barrel with the shroud and frame. Therefore, the barrel may be quickly removed from the frame and shroud by unscrewing it from the frame, the barrel flange 19t) prefera-bly having a hexagonal cross section to permit the application of a Wrench thereto for the purpose of rotating the barrel when threading or unthreading it with respect t-o the frame. Also, after the barrel 96 is disassembled from the frame and shroud, the crane 35 may be disconnected from the frame by swinging the cylinder from its recess 14 and then sliding the crane forwardly to remove the pivotal portion 38 thereof from its frame bore 20. Once the crane is removed from the frame, the cylinder 4t) may be removed from the crane by sliding the cylinder rearwardly with respect to the sleeve 46. Thus, both the cylinder and the barrel may be removed from the firearm to permit their replacement by another cylinder and barrel, respectively, to change the caliber of the fire- "arm, there being provi-ded in association with the firearm various matched sets of cylinders and barrels for this purpose. That is, there is provided a plurality of barrels generally similar yas shown at 95 but having different cal-iber bores, together with a corresponding plurality of cylinders, similar to that shown at 40, each of which is adapted for use with a particular one of said barrels and which is provided with cartridge chambers dimensioned lto receive cartridges having a caliber similar t-o that of the bore of the barrel with which the cylinder is associated. Therefore, each time a barrel is replaced with a different caliber barrel, the cylinder is yalso replaced with a new cylinder which corresponds in caliber with that of the new barrel.

The procedure for attaching a new barrel and cylinder to the firearm i-s substantially the reverse of the procedure used for removing the old barrel and the old cylinder. That is, the new cylinder is positioned on the sleeve 46 while the crane 36 is detached from the frame 10, then the crane is connected to the frame by positioning the pivotal portion 38 thereof in the frame bore 20, and then the cylinder is swung into its recess. Then the shroud 102 is positioned in front of the frame 10 and the crane 36 with the locking pin 106 positioned between the frame and the shroud and with the shroud bore in alignment with the threaded barrel-receiving bore of the frame. The new barrel is then slid longitudinally into the barrel bore and rotated in the proper direction to thread the rear portion thereof into connected relationship with the threaded frame bore and to bring the barrel flange into tight engagement with the forward face of the shroud 102 so that the shroud is held firmly in place between the forward face of the frame and the barrel flange 100.

As a precautionary measure, the relative sizes of the various interchangable cylinders and barrels are preferably such as to make impossible the matching of a small caliber barrel with a large caliber cylinder. In FIGS. l and 2, which show a barrel matched with a cylinder of the proper size, it will be noted that the rear portion of the barrel extends rearwardly beyond the rearwardly facing wall of the cylinder recess 14, as at 152, and is positioned in closely spaced relationship with the forward face of the cylinder 40. The distance which the barrel extends rearwardly beyond the rearwardly facing wall 150 of the cylinder recess is predetermined and is made to vary with the size of the barrel bore so that a barrel having a small -caliber bore will extend rearwardly beyond the wall 15) a greater distance than a barrel having a larger caliber bore. Likewise, the various cylinders 4t? are of different lengths so that when properly matched with the proper corresponding barrel, the close spacing between the forward face of the cylinder and the rear face of the barrel will be maintained. Thus, a cylinder having cartridge chambers dimensioned to receive large caliber cartridges will have a longer longitudinal length than a cylinder having cartridge chambers dimensioned to receive cartridges of a smaller caliber. From this, therefore, it will be evident that in the event a small caliber barrel were to be connected with the firearm at the same time as a larger caliber cylinder the forward face of the cylinder would be disposed at a location forwardly at the rear face of the barrel. Therefore, the barrel would interfere with the cylinder to prevent the cylinder from being swung to its normal operating position in the cylinder recess 14 and thus the firearm would be rendered inoperative in the event such a potentially dangerous mismatch between the barrel and the cylinder occurred. If the cylinder, prior to attaching the barrel, is in place within the recess 14, the mismatched smaller bore barrel would be tightened against the front face of the -cylinder to bind its action and thereby to prevent operation of the firearm. If a smaller ycaliber cylinder is put in place with a larger caliber barrel, the gun can be shot, but in this case a smaller caliber bullet will pass through the larger bore barrel, and in this case only minor accuracy will be lost and no danger will be involved.

The invention claimed is:

1. The combination in a firearm of: a frame, means defining a `cylinder recess in said frame having forward and rear walls and a bore in the forward wall for receiving the rear portion of a barrel, crane means for releasably receiving a cylinder and for supporting the same in said cylinder recess for rotation about a longitudinal axis, a plurality of barrels of differing caliber bores which barrels are selectively connectible with said frame and have rear portions which are receivable in said frame bore, and a cbrresponding plurality of cylinders which are selectively connectible with said crane and each of which cylinders corresponds with a respective one of said barrels and has a plurality of cartridge chambers dimensioned to receive cartridges of a caliber `similar to that of the corresponding barrel bore, each of said barrels when in connected relationship with said frame having the rear portion thereof extending rearwardly beyond the rear face of said forward frame wall by a predetermined distance which distance depends on the caliber of the barrel bore and is greater for a small caliber bore barrel than for a larger caliber bore barrel, and each of said cylinders having a predetermined length which depends on the caliber of the cartridges receivable by its cartridge chambers and which length is greater when the chambers are dimensioned to receive larger caliber cartridges than it is when the chambers are dimensioned to receive smaller caliber cartridges so that if a cylinder having chambers dimensioned to receive a larger caliber cartridge is connected to said crane at the same time as a barrel having a bore smaller than said last dimensioned caliber said cylinder will interfere with the rear end portion of said barrel to prevent said cylinder and crane from being moved to proper tiring position with respect to said crane.

2. The combination defined in claim 1 further characterized by all of said barrels having forward portions of substantially equal length and of substantially the same outside diameter and each barrel including a generally radially extending rearwardly facing surface spaced forwardly from its rear end portion, and a shroud 'having a bore adapted to receive a selected one of said barrels which shroud bore is of such a size and shape as to conform closely to the outside surfaces of said barrels while permitting a barrel to slide longitudinally and angularly with respect thereto during assembly and disassembly of said shroud with any one of said barrels, said shroud including a generally radially extending forwardly facing surface and being held in place on a selected barrel by engagement with said frame at its rear end and by the engagement of said rearwardly facing barrel surface with said forwardly facing shroud surface at a point spaced forwardly from said frame.

3. The combination defined in claim 2 further characterized by said frame bore being internally threaded and each of said barrels having external threads on its rear portion for threaded connection with said frame bore, the

engagement of the rearwardly facing surface on the connected barrel with the forwardly facing shroud surface limiting the threading movement of said barrel relative to said frame in the tightening direction to accurately locate the rear end of said barrel relative to said frame.

4. The combination in a firearm: a frame, means deining a cylinder recess in said frame having forward and rear walls and a bore in the forward wall for receiving the rear portion of a barrel, means for releasably receiving and supporting a cylinder in said cylinder recess of said frame for rotation about a longitudinal axis, a plurality of barrels of different caliber bores which barrels are selectively connectible with said frame and have rear portions which are receivable in said frame bore, and a corresponding plurality of cylinders which are selectively connectible with said releasable receiving and supporting means and each of which cylinders corresponds with a respective one of said barrels and has a plurality of cartridge chambers dimensioned to receive cartridges of a caliber similar to that of the corresponding barrel bore, Y

each of said barrels when in connected relationship with said frame having the rear portion thereof extending rearwardly beyond the rear face of said forward frame wall by a predetermined distance which distance depends on the caliber of the barrel bore and is greater for a smaller caliber barrel bore than for a larger caliber barrel bore, and each of said cylinders having a predetermined length which depends upon the caliber of the cartridges receivable by cartridge chambers and which length is greater when the chambers are dimensioned to receive larger caliber cartridges than when the chambers are dimensioned to receive smaller caliber cartridges so that when any one of said barrels is connected with said frame the space remaining in said cylinder recess is insutiicient to properly accommodate a cylinder having chambers dimensioned to receive cartridges of larger caliber than that for which the bore of the connected barrel is dimensioned.

No references cited.

BENJAMIN A. BORCHELT, Primary Examiner.

Claims

1. THE COMBINATION IN A FIREARM OF: A FRAME, MEANS DEFINING A CYLINDER RECESS IN SAID FRAME HAVING FORWARD AND REAR WALLS AND A BORE IN THE FORWARD WALL FOR RECEIVING THE REAR PORTION OF A BARREL, CRANE MEANS FOR RELEASABLY RECEIVING A CYLINDER AND FOR SUPPORTING THE SAME IN SAID CYLINDER RECESS FOR ROTATION ABOUT A LONGITUDINAL AXIS, A PLURALITY OF BARRELS OF DIFFERING CALIBER BORES WHICH BARRELS ARE SELECTIVELY CONNECTIBLE WITH SAID FRAME AND HAVE REAR PORTIONS WHICH ARE RECEIVABLE IN SAID FRAME BORE, AND A CORRESPONDING PLURALITY OF CYLINDERS WHICH ARE SELECTIVELY CONNECTIBLE WITH SAID CRANE AND EACH OF WHICH CYLINDERS CORRESPONDS WITH A RESPECTIVE ONE OF SAID BARRELS AND HAS A PLURALITY OF CARTRIDGE CHAMBERS DIMENSIONED TO RECEIVE CARTRIDGES OF A CALIBER SIMILAR TO THAT OF THE CORRESPONDING BARREL BORE, EACH OF SAID BARRELS WHEN IN CONNECTED RELATIONSHIP WITH SAID FRAME HAVING THE REAR PORTION THEREOF EXTENDING REARWARDLY BEYOND THE REAR FACE OF SAID FORWARD FRAME WALL BY A PREDETERMINED DISTANCE WHICH DISTANCE DEPENDS ON THE CALIBER OF THE BARREL BORE AND IS GREATER FOR A SMALL CALIBER BORE BARREL THAN FOR A LARGER CALIBER BORE BARREL, AND EACH OF SAID CYLINDERS HAVING A PREDETERMINED LENGTH WHICH DEPENDS ON THE CALIBER OF THE CARTRIDGES RECEIVABLE BY ITS CARTRIDGE CHAMBERS AND WHICH LENGTH IS GREATER WHEN THE CHAMBERS ARE DIMENSIONED TO RECEIVE LARGER CALIBER CARTRIDGES THAN IT IS WHEN THE CHAMBERS ARE DIMENSIONED TO RECEIVE SMALLER