Weapon Conversion Bolt Assembly Device

Abstract

A conversion bolt assembly for a hand carried weapon having automatic and semi-automatic or semi-automatic only modes of operation. The bolt assembly includes a tube having a fixed back plate on one end and longitudinally extending slots to permit spreading of the other end of the tube for assembly of the internal components. The internal components include a bolt having a firing pin and ejector assembled thereon, a recoil mechanism, an extractor affixed to the tube, and a trip for automatic operation actuable by the bolt. An external gas deflector is affixed to the bolt on a guiding projection extending through one of the slots in the tube. A removable cartridge barrel is provided at the other end of the tube.

Description

This invention relates to hand carried fire arms of the type adapted for automatic and semi-automatic operation, and is more particularly directed to the provision of a conversion bolt assembly and magazine for readily adapting a conventional weapon for the firing of ammunition of the type for which it was not originally designed.

In the past, it has been proposed to provide conversion devices for readily converting conventional weapons for the use of ammunition not normally acceptable by the weapon. There may be any of a number of reasons for the desirability of providing such conversion units. For example, U.S. Pat. No. 1,355,417 through U.S. Pat. No. 1,355,422 of John T. Pedersen disclose a conversion bolt assembly for readily converting a high power repeating military bolt action rifle for the semi-automatic firing of automatic pistol ammunition. The resultant device required modification of a standard military rifle, and since it was directed primarily to the conversion of a repeating bolt action rifle, the design employed is not readily adaptable to modern automatic/semi-automatic military rifles.

While other modification packages have been proposed that are more adaptable to weapons employed at this time, in general, such modification packages have been costly to produce and utilize.

The present invention is particularly directed to the modification of M-16 series assault rifles of the type employed by the United States Army. It will be obvious, of course, that the structures and concepts hereinafter disclosed may also be employed in combination with other weapons of similar operating features without departing from the spirit and scope of the invention.

The standard ammunition for an M-16 rifle is a 5.56mm cartridge. There are many occasions, however, when it may be desirable to employ other ammunition. For example, in the initial training of recruits, it may be more desirable to employ less expensive ammunition, and since many recruits are totally unfamiliar with high powered weapons, a gradual adjustment to such weapons by employing a a low powered subcaliber weapon may be beneficial to the overall process of familiarization with the weapons during training. It is also desirable on many occasions, for example in training, to employ lower cost cartridges. For example, the cost of .22 rim fire cartridges may be less than 10 percent of that of the standard 5.56mm cartridges.

While the barrel of a standard M-16 rifle is especially adapted for the 5.56mm military cartridges, the bore may be employed for the firing of any of a number of bullets having nominal .22 caliber. The chamber dimensions of the M-16 rifle, however, are not adapted for the firing of smaller ammunition, such as .22 LR ammunition, and consequently the concept of employing such smaller ammunition in a standard high powered weapon is feasible only with modification of the weapon, if the use of separate small caliber training weapons is to be avoided. It is further to be noted that the high powered standard ammunition for M-16 rifles is not desirable when the weapons are to be fired in indoor ranges, and in many cases adequate outdoor ranges for training and practice purposes are not available. In addition, the adaptation of a standard rifle to the firing of smaller ammunition may have advantages in some special military projects, such as in clandestine warfare. The subsonic .22 L.R. bullet may be silenced with a supressor, wherein the high velocity supersonic 5.56 mm bullet cannot be silenced due to the supersonic "crack."

If a standard military highpowered rifle is to be converted, there are a number of considerations which must be considered if the conversion is to be effective. For example, the conversion should be accomplished as simply as possible, and not require basic modification of the standard weapon. In addition, it is desirable for any conversion devices to be as inexpensive and simple as possible, and be readily and easily servicable. It is further desirable that a converted weapon have substantially the same characteristics in firing and use as the standard weapon, in order that training in the use of a converted weapon leads naturally to familiarization with unconverted devices.

It is therefore an object of this invention to provide a conversion bolt assembly that is readily adaptable for use on a standard rifle, and that provides the above recited characteristics necessary to the effective conversion of a highpowered fire arm. According to the invention, a rifle, preferably of the type adaptable for automatic and semi-automatic modes of operation, is adapted to the firing of a smaller and lower powered ammunition, by providing a unitary bolt assembly that may be easily and readily substituted for the standard bolt assembly in the weapon. Further in accordance with the invention, the only other modification required for conversion of the standard weapon, is the insertion by standard technique of a magazine assembly adapted to carry the smaller ammunition.

According to the invention, the conversion bolt assembly consists of a tube formed of a resilient material such as cold rolled steel. A backing plate is permanently affixed in one end of the tube. The tube has upper and lower longitudinally extending slots, so that the other end thereof may be readily sprung apart to permit assembly of the components in the tube. A recoil spring assembly is provided within the tube, abutting the back plate, and cooperating with a sliding bolt in the chamber. The sliding bolt carries a firing pin, and an extractor mechanism. An ejector device is removably affixed to the tube, and has an ejector blade extending into a slot in the bolt. A short cartridge barrel is removably affixed in the other end of the tube, providing therein a chamber for the smaller ammunition. In order to enable automatic operation, a slide is provided in the tube, which cooperates with the standard automatic sear in the weapon itself. The sliding bolt has a projection for engaging the trip for the automatic sear.

The conversion bolt assembly is shaped so that its insertion in the weapon requires only the simple removal of the standard bolt and replacement by the conversion bolt assembly, and the operation of the weapon in the normal fashion is not affected by employing the conversion bolt assembly. The device is self contained, and does not employ the weapons normal buffer and recoil spring in operation, nor does it require removal of such buffer and recoil spring from the standard weapon.

According to a feature of the invention, the short chamber barrel is provided with a pair of lugs for engaging holes in the end of the tube. This permits ready assembly and disassembly of the chamber barrel, as well as the opening of the end of the tube for disassembly of the remaining components. In addition, such construction permits some movement between the chamber barrel and the tube to compensate for manufacturing tolerances in misalignment between the chamber and the bolt recess in the receiver of the weapon.

By providing a back plate on the tube, and employing a recoil spring assembly within the tube, the recoil may be designed in accordance with the ammunition which is to be employed with the device. It is thus not necessary to provide any modification of the recoil spring of the weapon itself, and the recoil spring and buffer of the weapon cooperate with the conversion bolt assembly to continually urge the chamber barrel of the conversion unit against the chamber of the weapon to prevent the escape of gas during firing.

Further, in accordance with the invention, the upper portion of the tube is formed with flat "bent-in" sections forming guide ribs for the upper slot. These guide ribs engage slots in the bolt for guiding the bolt, as well as forming stiffeners for the receiver tube. A projection on the bolt extending through the upper slot in the tube is connected to an outer gas deflector, which cooperates with the charging handle of the weapon in the manual operation of the bolt, the deflecting of firing gases from striking a shooter, and in urging the bolt backward as a result of gas pressure during firing for automatic and semi-automatic operation. The gas deflector may also serve as a cover for the firing pin slot in the bolt, to prevent dirt from entering the slot.

The ejector is preferrably rigidly held in the tube by means of knife edges forming the edges of a transverse slot in the tube, so that the ejector can be removed by downward force on the ejector, thereby camming the sides of the tube apart. The ejector is preferably spaced in the tube to serve in addition as a barrier for forward travel of the trip for the automatic sear.

In accordance with the preferred embodiment of the invention, the automatic trip is in the shape of a "window frame," the central aperture thereof cooperating with a downward projection on the bolt for the necessary movement of the trip. Since the trip does not reciprocate completely with the movement of the bolt, this arrangement avoids undesirable addition of weight to the recoiling members of the device and the weapon. In addition, this form of trip requires no complicated mounting slots or pins, since it is simply held in assembly by the inside walls of the tube.

The modified magazine assembly employed with the conversion bolt assembly of the invention may be of standard configuration for the weapon, merely being adapted to hold and feed the smaller ammunition.

The invention will now be described in greater detail with reference to the accompanying drawings, in which:

FIG. 1 is a side view of a conventional weapon of the form in which the device of the present invention may be employed;

FIG. 2 is a partially cross-sectional view of a portion of the weapon of FIG. 1;

FIG. 3 is an exploded perspective view of the components of a bolt assembly according to the invention;

FIG. 4 is a partially cross-sectional view of a portion of a weapon corresponding to that shown in FIG. 2, but in which the bolt and magazine have been replaced by a conversion bolt assembly and modified magazine according to the invention;

FIG. 5 is a top view of the assembled tube and back plate of the assembly of FIG. 3;

FIG. 6 is a right side view of the assembly of FIG. 5;

FIG. 7 is a bottom view of the assembly of FIG. 5;

FIG. 8 is a cross-sectional view of the assembly of FIG. 6 taken along the lines 8--8;

FIG. 9 is a cross-sectional view of the assembly of FIG. 6 taken along the lines 9--9;

FIG. 10 is a partially cross-sectional end view of the assembled buffer, recoil spring and recoil spring guide of FIG. 3 taken along the lines 10--10 of FIG. 11;

FIG. 11 is a partially cross-sectional view of the assembly of FIG. 10 taken along the lines 11--11;

FIG. 12 is a top view of the bolt of the assembly of FIG. 3;

FIG. 13 is a right side view of the bolt of FIG. 12;

FIG. 14 is a bottom view of the bolt of FIG. 12;

FIG. 15 is a longitudinal cross-sectional view of the bolt of FIG. 12 taken along the lines 15--15;

FIG. 16 is an end view of the left end of the bolt of FIG. 12;

FIG. 17 is an end view of the right end of the bolt of FIG. 12;

FIG. 18 is a transverse cross-sectional view of the bolt of FIG. 13 taken along the lines 18--18;

FIG. 19 is a transverse cross-sectional view of the bolt of FIG. 12 taken along the lines 19--19;

FIG. 20 is a cross-sectional view of a portion of a bolt taken along the lines 20--20 of FIG. 17;

FIG. 21 is a top view of the chamber barrel of the assembly of FIG. 3;

FIG. 22 is a right side view of the chamber barrel of FIG. 21;

FIG. 23 is an end view of the left end of the chamber barrel of FIG. 22;

FIG. 24 is an end view of the right end of the chamber barrel of FIG. 22;

FIG. 25 is an enlarged cross-sectional view of the chamber barrel of FIG. 21 taken along the lines 25--25;

FIG. 26 is a cross-sectional view of a modification of the chamber barrel of FIG. 25 taken along the lines 26--26;

FIG. 27 is a side view of a firing pin of the assembly of FIG. 3;

FIG. 28 is a cross-sectional view of a portion of the firing pin of FIG. 27 taken along the lines 28--28;

FIG. 29 is a side view of the trip of the assembly of FIG. 3;

FIG. 30 is a top view of the trip of FIG. 29;

FIG. 31 is an end view of the left end of the trip of FIG. 29;

FIG. 32 is an end view of the right end of the trip of FIG. 29;

FIG. 33 is a right side view of the ejector of the assembly of FIG. 3;

FIG. 34 is a top view of the ejector of FIG. 33;

FIG. 35 is an end view of the right end of the ejector of FIG. 33;

FIG. 36 is a partially cross-sectional view of a portion of an assembled bolt assembly according to the invention;

FIG. 37 is an enlarged cross-sectional view of the bolt of FIG. 36 taken along the lines 37--37, and including in dashed lines the relative position thereof with respect to the charging handle slot of a weapon including the device;

FIG. 38 is a partially cross-sectional view of a modified magazine which may be employed in combination with the conversion bolt assembly according to the invention;

FIG. 39 is a side view of the magazine assembly of FIG. 38;

FIG. 40 is a top view of the magazine assembly of FIG. 38;

FIG. 41 is a partially cross-sectional top view of the bolt assembly according to the invention, illustrating a cartridge in place in a chamber barrel preparatory to firing;

FIG. 42 is a cross-sectional view of a portion of the assembly of FIG. 41 illustrating the relationship of the components shortly after firing; and

FIG. 43 is a partially cross-sectional view of a portion of the assembly of FIG. 42 illustrating the ejection of the cartridge casing shortly after the position of the components as illustrated in FIG. 42.

DETAILED DESCRIPTION OF THE CONVERSION BOLT ASSEMBLY

Referring now to the drawings, and more in particular to FIG. 1, therein is illustrated a typical conventional weapon which may employ the conversion device according to the invention. The illustrated weapon is a standard M-16 rifle, and includes an upper receiver 50 hinged to a lower receiver 51 at a pivot pin 52. A removable pin 53 extends through the lower receiver to hold the upper receiver 50 in place. A charging handle 54 at the rear of the upper receiver is provided for charging the device, and for removing the bolt 55 when the upper receiver is swung free of the lower receiver. Automatic and semi-automatic operation of the weapon is achieved by means of a gas tube 56 (illustrated in dash lines in FIG. 1) extending from a forward portion of the barrel 57 to the receiver. A removable ammunition clip 58 is inserted in the lower receiver.

The portions of the weapon of FIG. 1 which are of interest in the detailed explanation of the present invention are illustrated in simplified form in cross-section in FIG. 2. This Figure illustrates the upper receiver 50 having a hinge aperture 65 for receiving the hinge pin 52, and a downwardly extending boss 66 having an aperture 67 for receiving the retaining pin 53. The gas tube 56 extends through the front of the upper receiver 50 and enters a gas chamber 68 for affecting the backward movement of the bolt upon the firing of a round. The bolt 55, upon firing, moves backwardly into the gunstock 69 (FIG. 1) against the action of a recoil spring 70 and buffer 71 in the stock. The charging handle 54 slidably extends into the upper receiver, and carries a projection 74 which engages a projection 72 on the bolt upon rearward movement of the charging handle 54, to affect the manual charging of the weapon. The charging handle 54 also has an elongated internal slot 73 for clearance of the bolt during operation of the weapon. An automatic sear 75 of conventional nature is provided in the lower receiver according to the conventional practice. The sear 75 is operated by the bolt 55, for catching an upper hook 78 of the weapons hammer 77 during automatic operation of the device. In semi-automatic operation the trigger mechanism (not shown) of the device catches the lower hook 79 of the hammer.

In order to remove the bolt assembly 55 from the receiver in the device of FIGS. 1 and 2, the take down pin 53 is removed, after the weapon is cleared, and the upper receiver 50 is swung away from the lower receiver about the pivot pin 52. The charging handle 54 may then be pulled in a rearward direction, so that the flange 51 engages the flange 72 on the bolt assembly, thereby pulling the bolt assembly out of the receiver. FIG. 2 also illustrates a cartridge 76 in firing position in the firing chamber of barrel 57. The magazine 58 is held in the lower receiver, by means not illustrated, so that cartrides are fed from the top of the magazine upon forward movement of the bolt 55.

The components of the conversion bolt assembly according to the present invention are illustrated in the exploded perspective view of FIG. 3, and in assembled form in the partially cross-sectional view of FIG. 4. Referring now to FIGS. 3 and 4, the conversion bolt assembly is comprised of a tube 85 having a back plate 86 secured therein at its rearward end. The back plate 86 may be held in the tube 85 by any conventional means, such as for example, by brazing. The combination of the tube 85 and back plate 86 is more clearly illustrated in FIGS. 5 through 9.

Referring now to FIGS. 5 - 9, the lower portion of the tube 85 is circular, and the upper portion has a flattened surface 87 through which a slot 88 extends for the entire length of the tube. An ejection port 9 is provided on the right hand side of the tube in the forward portion thereof. A pair of pin holes 90 are provided on opposite sides of the tube at the forward end thereof. In addition, a slot 91 extends from the forward end of the bottom of the tube to the proximity of the rearward end. (The noted directions in the description of the device refer to the position of the structure with respect to their position in an assembled weapon) A transverse slot 92 is provided in the bottom of the tube adjacent the rear end of the ejection port 89, and a further transverse slot 93 is provided in the bottom of the tube rearwardly of the slot 92. The back plate 86 generally conforms to the internal shape of the tube 85, and has an upward projection 95 extending above the flat upper surface 87, the sides of the projection 95 being grooved to receive the rear portions of the surface 87. The back plate 86 may be provided with a central aperture 96.

The tube 85 is preferably formed of a resilient material, such as cold rolled steel, so that the forward ends of the tube may be sprung apart without the use of tools, due to the provision of the opposed slots 88 and 91 thereby permitting assembly and disassembly of the other components of the bolt assembly of the invention in the forward end of the tube. In other words, the tube forms a U-shaped spring member. The flattened surfaces 87 on the upper side of the tube may be formed as two "bent-in" sections, and these bent-in sections form guide ribs on opposite sides of the slot 88 for guiding the bolt, as will be explained in more detail in the following paragraphs. In addition, the two bent-in portions of the tube act as stiffeners for the tube, to make the tube rigid and strong with the resultant prevention of distortion. Furthermore, the bent-in sections permit clearance between the conversion bolt assembly according to the invention and the lower portion of the charging handle 54 of the weapon, while still maintaining sufficient material for adequate strength in the region of the tube 85 above the ejection port 89. The projection 95 on the back plate 86 is shaped to enter the bolt carrier-key recess in the upper receiver of the weapon, thereby orienting the device in the upper receiver during assembly. As will be explained more fully in the following paragraphs, the lower slot 91 forms an opening for the magazine, the hammer, and the automatic trip, during operation of the device.

Referring again to FIGS. 3 and 4, a buffer block 100, for example of a polyurethane material, is provided in the rear of the tube abutting the back plate 86. The block 100 is provided with an aperture 101 through which a recoil spring guide 102 surrounded by a recoil spring 103 extend. The rear end of the recoil spring guide may be enlarged to retain the end of the spring 103. This sub-assembly is more clearly illustrated in FIGS. 10 and 11.

Referring again to FIGS. 3 and 4, a bolt 110 is assembled in the tube 85 for longitudinal sliding movement therein. The configuration of the bolt is more clearly illustrated in FIGS. 12-20.

Referring now to FIG. 3 and FIGS. 12-20, the bolt is a unitary member having a generally D-shaped right hand side 111 and generally D-shaped left hand side 112 for slidably engaging the interior of the tube 85, the forward portions of the D-shaped members 111 and 112 being joined by a bridge 113, so that a space 145 exists between the rear portions of the D-shaped members for clearing the hammer of the weapon. A central longitudinally extending firing pin slot 114 is provided in the upper portion of the bridge 13, and a longitudinally extending ejector slot 115, displaced from the center of the bolt, is provided in the lower portion of the bridge 113. A longitudinally extending recoil spring bore 116 is provided in the left hand D-shaped member 112, the front of the bore having a reduced diameter portion 117, as shown in FIGS. 17 and 20, the portion 117 having a diameter to permit passage therethrough of the recoil spring guide, with the shoulder between the bore 116 and the portion 117 serving as a front stop for the recoil spring 103 (see FIG. 3).

Referring again to FIGS. 12-20, a cover detent recess 120 is provided in the side of the right hand D-shaped member 111, and a transverse firing pin retaining pin bore 121 extends through the bolt from the recess 120 through both D-shaped members 111 and 112 and the bridge 113. One end of the bore 121 may be enlarged, as shown at numeral 122 in FIG. 19 for retaining the head of a pin. A longitudinally extending extractor slot 125 is provided in the right hand D-shaped member 112 extending from the front end of the bolt, but preferrably not extending for the full length of the bolt. As illustrated in FIGS. 17-19, the slot 125 extends in a plane passing through the center of the bolt, and may extend from the outside of the bolt at a slightly downward angle. An extractor pin bore 126 extends transversely of the slot 125 in the right hand D-shaped member 111, as illustrated most clearly in FIG. 19. The upper end of the bore 126 may be enlarged at 127 for retaining the head of an extractor pin. An extractor spring hole 128 extends partially through the bolt from the extractor slot 125 rearwardly of the extractor pin bore 126. As illustrated in FIGS. 3 and 36 a longitudinally extending bore 130 is provided in the rear of right hand D-shaped member 111, this bore only extending partway through the bolt. As illustrated in FIG. 12, a transverse aperture 131 is provided in the rear of the D-shaped member 111 extending through the bore 130.

Still referring to FIGS. 12-20, the upper portion of the bolt has a flat surface 135 conforming to the flat inner shape of the top of the tube 85, for slidably engaging the inner surface of the tube, and the bridge 113 has an upwardly extending portion 136 which is adapted to extend through the slot 88 of the tube 85. The central portion of the front of the bolt is provided with a clearance 138 for the head of a cartridge. The lower portion of the bolt also has flattened surfaces 139 for engagement with the upper surface of a trip device to be more fully explained in the following paragraphs, the rear portion of the bolt having a downwardly extending portion 140 with front edges 141 for engaging the slot of the trip device. The forward central portion of the bottom of the bolt may be recessed, as shown at 143, to provide clearance for the top of the magazine. The rear edge 144 of the bridge 113, which engages the hammer of the weapon during recoil, may be bevelled at the bottom, as shown in FIG. 15.

Referring again to FIGS. 3 and 4, the bolt 110 is assembled in the tube 85 with the recoil spring guide 102 and the recoil spring 103 extending through the bore 116 of the bolt. A chamber barrel 150 is removably held in the front of the tube 85, for example by means of retainIng lugs 151 adapted to extend through the holes 90 in the sides of the tube. The lugs 151 may be in the form of pins inserted in pin holes in the chamber barrel. The chamber barrel is more clearly illustrated in FIGS. 21-26, wherein it is seen that this element is comprised of a rear block portion 154 shaped to be received in the front end of the tube 85, and a front portion 155 in the shape of a cartridge of the type adapted to be normally employed in the weapon in which the conversion device of the invention is to be employed. As illustrated in FIGS. 21-24, the lugs 151 extend from opposite sides of the block portion 154, while the cross-sectional view of FIG. 26 illustrated pin holes 153 which may be employed for holding the lugs. The lugs 151 are preferably not easily removable from the chamber barrel. The upper portion of the block 154 has an upwardly extending alignment portion 152 for engaging the slot 88 of the tube 85. The side of the chamber barrel 150 is provided with a bevelled slot 156, aligned with the extractor slot 125 of the bolt, and the rear end of the chamber barrel is provided with a lower feed ramp 157. Referring to FIGS. 25 and 26, a bore 158 extends longitudinally within the chamber barrel 150. The rear portion 159 of the bore 158 is shaped to fit a cartridge of the type adapted to be fired in the weapon when the conversion device of the invention is employed, and the front portion 166 of the bore 158 forms a short barrel for a bullet of the caliber to be employed with the weapon employing the conversion bolt. Since the diameter of the bullet employed with the conversion device is essentially the same as that fired in an unconverted weapon, there is a relatively smooth transission between the portion 166 of the chamber barrel 150 and the rifled bore of the barrel 57 of the weapon illustrated in FIG. 1.

The chamber barrel 150 is adapted to be assembled in the end of the tube 85 by merely spreading the ends of the tube and inserting the chamber therein until the assembly snaps together with the holes 90 engaging the lugs 151. This arrangement permits some movement between the chamber barrel and the tube, thereby compensating for manufacturing tolerances so that the chamber barrel 150 may be firmly held in position in the chamber of the weapon. Other advantages of the invention will be pointed out in the following paragraphs.

Referring again to FIG. 3, a firing pin 160 is assembled firing pin slot 114 of the bolt 110. As shoWn in FIGS. 27 and 28, the firing pin is comprised of an elongated plate shaped to fit the slot 114, the front 161 of the firing pin having reduced dimensions to form a generally rectangular end 162 adapted for firing engagement a cartridge. As shown in FIG. 4, the conversion device specifically disclosed herein is adapted for firing rim fire cartridges, so that the lower portion of the end 162 engages the rim of a cartridge 163 in the chamber of the chamber bore 150 during firing. A transverse slot 164 is provided in the firing pin 160 (as shown in FIGS. 3, 4 and 27) for receiving a firing pin retaining pin 165 which extends through the retaining pin bore 121 of the bolt. The slot 164 is elongated to permit slight forward and reverse movement of the firing pin in the bolt. As illustrated in FIG. 4, when the firing pin is in its rearmost position, it projects slightly into the space 145 between the two D-shaped members 111 and 112 of the bolt. The hammer 77 of the conventional weapon may thus be triggered to move into this space to strike the end of the firing pin, and hence to fire the weapon.

Referring again to FIGS. 3 and 4, a sliding trip 170 is provided in the tube 85, with the upper flat surface of the trip 170 slidably engaging the lower flat surface 139 of the bolt. As illustrated in FIGS. 29 through 33, the trip 170 has a flat upper surface, with a rectangular central aperture 171 as shown in the top view of FIG. 30. The aperture 171 is shaped so that the downward projection 140 of the bolt extends therethrough. The sides of the trip 170 are shaped to slidably conform to the lower inside surface of the tube 85. A downward projection 172 is provided at the rear of the trip, the projection 172 being shaped to extend through the lower slot 91 in the tube 85, for cooperation with the automatic sear 75 provided on the standard weapon. In other words, as illustrated in FIG. 4, the automatic sear 75 extends into the aperture 171, so that the rear edge 174 of the aperture 171 can engage the automatic sear. The front edge of the projection 172 is bevelled to cam the automatic sear out of the way when the upper receiver of the weapon is closed on the lower receiver during conversion of the weapon. The front edge 175 of the rectangular aperture in the trip, as will be described in more detail in the following paragraph, is adapted to be engaged by the front edge 141 of the downward projection 140 of the bolt, when the bolt is moved to its forward position. The top of the front web 176 of the trip may be concave, as illustrated in FIG. 32.

The trip 170 thus forms a connector between the short bolt of the conversion device according to the invention, and the automatic sear of the weapon. Due to the "window frame" construction of the trip, the trip is easily assembled and disassembled in the conversion bolt assembly, and no complicated mounting slots or pins need be employed to hold it in position, since it slides between the inside of the tube 85 and the lower edges of the bolt, with its forward movement being inhibited by the ejector, as will be discussed in more detail in the following paragraphs. As will be apparent, the trip 170 does not reciprocate during operation of the weapon, with the bolt.

Referring again to FIG. 3, an ejector 180 is mounted in the bottom of the tube. The ejector 180 is more clearly illustrated in FIGS. 33 - 35, wherein it is seen that the ejector is formed of a mounting base 181 and an ejector blade 182. The base 181 is formed to fit in the slot 92 of the tube 85, and thus has lower side portions 183 conforming to the outer circumference of the tube 85. The edges of the slot 92 of the tube 85 are formed as knife edges, as seen in FIG. 37, and the sides of the ejector 180 are formed with recesses 184 which match the knife edges of the tube. The length of the base 181 conforms to the length of the slot 92. The ejector blade 182 extends upwardly from the base 181 and into the ejector slot 115 of the bolt 110 to permit relative sliding movement therein. The forward upper edge of the ejector blade 182 is formed to serve as an ejector for a cartridge case being extracted during operation of the device.

The above described structure for the ejector provides a number of advantages. The ejector is rigidly held in the tube by the knife blades formed at the edges of the slot 91. In order to remove the ejector from the tube, the ejector may be pushed downwardly, so that the knife edges of the tube are cammed outwardly to permit downward removal of the ejector. The ejector may be assembled in the tube by spreading the ends of the tube apart, without the necessity for employing tools. The ejector is thus held rigidly in the assembly inside of the weapon, yet may easily be assembled and disassembled. As above stated, the ejector 180 also serves as a forward stop for the trip 170.

Referring again to FIG. 3, an extractor 190 is assembled in the extractor slot 125 of the bolt. The extractor 190 is a lever pivoted by means of an extractor pin 191 extending through the extractor pin bore 127 in the bolt 110. The front end of the extractor 190 is provided with a hook 192 for engaging a shell casing, and an extractor spring 193 in the extractor spring hole 128 urges the rear end of the extractor 190 generally outwardly of the device, thereby urging the hook 192 into latching engagement with the edge of a shell casing. When the bolt is in the foremost position, the front hook 192 of the extractor enters the slot 156 of the chamber barrel 150 to engage the cartridge.

Referring to FIGS. 3 and 4, a gas deflector 200 is permanently affixed to the top of the bolt 110. The gas deflector 200 is comprised of a flat plate 201 mounted on top of the projections 136 of the bolt, thereby covering the firing pin slot 114 as seen in FIGS. 36 and 37) and inhibiting dirt from entering the slot 114. An upward projection 202 at the rear of the gas deflector forms a gas barrier inside the recess 73 of the charging handle, as seen in FIG. 4, so that gas entering the chamber from the gas tube 56 urges the bolt 110 backwardly and deflects the gas from being discharged to the rear of the receiver, and thereby striking the operator. The gas deflector 200 is wider than the slot 88 in the tube 85 so that it forms the top surfaces of guide slots in the bolt assembly for the bolt, as defined by the flat upper surfaces 135 of the bolt, projections 136 of the bolt, and the lower edges of the gas deflector 200 as shown more clearly in FIG. 37. The front edge 203 of the gas deflector extends forwardly of the bolt, and as illustrated in FIG. 4, cooperates with the front projection 74 on the charging handle for drawing the bolt 110 rearwardly, and for extracting the conversion device when the upper receiver is swung open as previously described. The gas deflector may be affixed by any suitable means, such as brazing, to the top of the bolt.

Referring again to FIG. 3, suitable weights, such as cylindrical front weight 210 and cylindrical back weight 211 are assembled in the bore 130 in the back of the bolt, the weights being separated by a polyurethane disk 213. The weights are held in place by a weight retaining pin 214 inserted in aperture 131 at the rear of the bolt.

ASSEMBLY AND DISASSEMBLY OF THE CONVERSION BOLT

Since a number of features and advantages of the invention involve the assembly of the above described bolt assembly components, the assembly and disassembly of this structure will now be described.

The back plate 86 is preferably preassembled in the end of the tube 85, for example, by means of brazing. The tube 85 is preferably formed of a material such as cold rolled strip steel, so that due to its upper and lower slots 88 and 91, respectively, it forms a U-shaped spring. The buffer 100 may first be inserted in the tube to its position adjacent the back plate 86. The trip 170 may then be inserted in the tube, with the lower projection extending through the back of the roller slot 91. The front ends of the tube are then swung apart, to separate the knife edges formed by the transverse slot 92, to permit insertion of the ejector 180 in the slot. It is seen that the ejector 180 thus forms a forward stop for the trip 170. In disassembly, as above described, the ejector is removed by downward pressure, thereby camming the sides of the tube apart. The recoil spring guide 102 and recoil spring are then assembled and inserted in the aperture 101 in the buffer 100.

The firing pin 160 and its retaining pin 165, the extractor spring 193 and extractor 190 and its retaining pin 191, and the weights 210 and 211, disk 213 and retaining pin 214 are assembled in their respective positions in the bolt 110, and this assembly may then be inserted in the forward end of the tube 85 with the recoil spring guide 102 and recoil spring 103 extending through the bore 116. As above noted, the retaining lugs 151 of the chamber barrel 150 may be permanently in position in the chamber barrel. In order to assemble the chamber barrel on the tube, the forward end of the tube 85 is sprung apart, and the chamber barrel inserted therein until the pins 151 are lined with the holes 90, then the forward ends of the tube are permitted to snap back to hold the chamber barrel in place. It is to be noted that the chamber barrel is loosely pivoted in the end of the tube 85. This permits some movement and pivoting between the barrel and the tube 85. Such movement is advantageous, since it allows for manufacturing tolerance misalignments between the chamber and the bolt recess in the receiver of the weapon. Thus, the chamber barrel 150 is held positively in position in the weapon, since it is impossible for the tube 85 to unsnap over the lugs 151 when the device is positioned inside of the receiver of the weapon. The barrel 150, however, may easily be assembled and disassembled from the device without the use of tools.

In disassembly, the sides of the tube 85 are sprung apart to permit removal of the chamber barrel. The internal components of the device may then be removed from the end of the tube in the order reverse to the order of assembly.

The above described assembly and disassembly of the device thus may all be achieved from the forward end of the assembly. This is desirable, since it allows the comparatively heavy bolt to be employed as a tool to assembly the recoil spring, and also allows the comparatively heavy bolt to be employed as a tool in disassembly of the recoil spring. Since the device is assembled and disassembled from the forward end, there is easy access to the surfaces requiring the most cleaning, i.e., the inside of the tube 85 nearest the breech and the breech face itself.

MAGAZINE ASSEMBLY

Since the weapon modified with the above described conversion device employs different, i.e. smaller, ammunition, a modification is also required in the magazine assembly. This modification is illustrated in FIGS. 38 - 40. Referring now to these Figures, the outer casing 250 of the magazine is in the shape conventionally employed in the weapon, and hence its form and means for being retained in the weapon are conventional and need not be discussed herein. The magazine is modified by providing a well 251 therein, the well 251 being shaped to conform to the new form of ammunition. The well 251 is held in the magazine by suitable upper and lower closures 252 and 253 respectively, and may be held to the edge of the magazine by a tab 254 rivetted to the magazine. The well 251 includes a follower assembly 255 and a spring 256 for feeding the cartridges upwardly in the conventional fashion.

CONVERSION OF THE WEAPON

In order to convert a standard weapon, such as a standard U. S. rifle caliber 5.56mm, M-16, to fire miniature ammunition, such as caliber .22 long rifle ammunition, employing the conversion device of the invention, the weapon is of course first cleared of ammunition according to conventional techniques. Referring to FIG. 1, the takedown pin 53 is then removed, so that the upper receiver 50 can swing away from the lower receiver 51 about the pivot pin 52. The charging handle 54 is then pulled backwardly, so that the standard bolt assembly is pulled part way out of the receiver, and the bolt can be manually grasped and pulled completely out of the receiver. The conversion bolt assembly is then inserted in the receiver, and pushed into the receiver as far as possible. In this position, the chamber barrel 150 of the conversion device has entered the chamber of the weapon. The upper receiver is then closed on the lower receiver, and the takedown pin 53 is pushed into locking position. A new magazine, of the form illustrated in FIGS. 37-39 is then inserted in the regular magazine of the weapon. The entire conversion of the weapon may thus be accomplished in a very short period of time.

When the conversion unit is assembled in the receivers of the weapon, the projection 95 on the back plate enters the bolt carrier-key recess in the upper receiver of the weapon, thus orienting the device in the upper receiver in assembly. The back plate 86 contains the weapons buffer 71 in the reassembled weapon. The buffer 71 of the weapon thus maintains a forward pressure against the back plate 86 at all times. This pressure takes up any longitudinal slack between the conversion device according to the invention and the weapons receiver. The front shoulder of the block 154 of the chamber barrel 150 is thus held against the inside of the chamber of the weapon at all times, thereby preventing escape of gas during firing of the weapon. As above noted, the bevelled edge of the projection 172 of the trip 170 urges the automatic sear out of the way when the upper receiver is closed on the lower receiver.

OPERATION

In the operation of a weapon, such as an M-16, converted in accordance with the present invention, and assuming initially that the weapon selector has been set to provide semi-automatic operation (i.e. the automatic sear 75 is inoperative), and further assuming that there is no cartridge in the receiver, the weapon is initially charged by pulling back and releasing the charging handle 54. As illustrated in FIG. 4, with this action, the backward movement of the projection 74 on the front of the charging handle engages the front edge 203 of the gas deflector, so that backward movement of the charging handle carries the bolt backward against the force of the recoil spring 103. The backward movement of the bolt forces the hammer of the weapon into cocked position. When the charging handle is released, the recoil spring moves the bolt forwardly, to engage a cartridge in the end of the magazine, and to force it forward up the feed ramp 157 and into the chamber. As the bolt moves to its forward position against the block 154 of the cartridge barrel 150, the hook 192 on the extractor is urged into a hooking relationship with the rim of the cartridge case, as illustrated in the position shown in FIG. 41. The weapon is now in condition to fire the first round.

When the trigger of the weapon is pulled, the hammer 77 in the weapon is released by the conventional mechanism, to swing upwardly into the space 145 between the D-shaped members 111 and 112 of the bolt, and to thereby strike the projecting end of the firing pin 160. The end 162 of the firing pin strikes the rim of the cartridge to effect the firing thereof, so that the bullet is forced through the short end barrel 155 of the chamber barrel 150 and thence into the barrel 57 of the weapon. When the bullet has traveled for sufficient distance down the barrel 57, the firing gases are directed from the barrel into the gas tube 56 of the conventional weapon. This gas is expelled into the receiver of the weapon, and the pressure acting on the bolt and the gas deflector projection 202 forces the bolt backwardly against the force of the recoil spring 103. The initial stage in the backward movement of the bolt is illustrated in FIG. 42, wherein it is seen that the hook 192 on the extractor, which engages the rim of the cartridge, effects the removal of the cartridge casing from the chamber barrel 150, this backward movement continuing until the end of the cartridge casing strikes the ejector blade 182. Since the ejector blade 182 is offset from the axis of the barrel, as the bolt continues its rearward movement, the fixed ejector blade effects the rotation of the rear of the cartridge casing, as illustrated in FIG. 42, so that the cartridge casing is released from the extractor hook 192 and ejected from the weapon through the port 89 in the tube 85. It is to be noted that the backward movement of the bolt is resisted only by the recoil spring 103 in the conversion bolt, and the recoil spring 70 of the weapon itself is not active in the operation of the conversion bolt. In other words, the conversion bolt assembly according to the invention is completely self contained with respect to the recoil of the bolt.

As in the initial charging of the weapon, during the rearward movement of the bolt the rear end of the bridge 113 of the bolt forces the hammer to pivot downwardly into cocked position clear of the bolt. In its rearmost position, the bolt strikes the buffer, to absorb the remaining shock of the backward movement. Since the gas deflector projection 202 extends upwardly into general conformity with the shape of the slot 73 in the charging handle as shown in FIG. 37, the firing gases are prevented from discharging to the rear of the receiver, and thus when the bolt has moved sufficiently backwardly, the gases are expelled through the port 89. In semi-automatic operation of the weapon, the automatic sear 75 of the weapon is moved out of position with respect to the hammer, and thus this component of the weapon, and the trip 170 of the conversion bolt assembly, do not enter into the operation of the weapon.

When the energy expended in moving the bolt backwardly is expended, the recoil spring 103 urges the bolt to move in the forward direction toward the chamber barrel 150. During this forward movement, the front of the bolt 110 engages the rear end of a new cartridge in the end of the magazine, and urges the cartridge up the feed ramp 157 and into firing position in the end of the chamber barrel 150. The weapon is then prepared to fire a new round upon reactuation of the trigger of the weapon.

In automatic operation of a weapon employing the conversion bolt assembly according to the invention, the automatic sear 75 and hammer 77 of the weapon operate in their normal fashion in the weapon. In other words, when the selector switch of the weapon is set to automatic operation, and the trigger is held backward continually, the automatic sear 75 engages the upper catch 78 on the hammer to hold the hammer until it is released due to forward movement of the bolt, and this action continues as long as the trigger is held back. When the trigger is released, the lower catch 79 of the hammer is held by the trigger assembly. In the arrangement according to the present invention, the trip 170 is provided to effect the proper operation of the automatic sear. When the trigger is released, the normal latching with the latch 79 of the hammer 77 is operative.

Assume now that the weapon, converted with the conversion bolt assembly, is set for automatic operation.

The release of the hammer for the firing of the first round is similar to that above described, with the bolt being moved backwardly and the cartridge case being ejected in the same manner as previously described. As the bolt moves backwardly, the downward projection 140 of the bolt moves backwardly in the rectangular slot 171 of the trip whereby the front edge 141 of the projection moves out of engagement with the front edge 175 of the recess. This releases the trip and hence the automatic sear, so that the sear may catch the hammer. When the bolt moves forwardly during recharging of the weapon, the projection 140 of the bolt moves forwardly in the rectangular recess 171 of the trip, until, near the forwardmost position of the bolt, it strikes the front edge 175 of the trip, thereby carrying the trip 170 forward a short distance. The rear edge of the rectangular recess 171 and the downward projection 172 thereof, thereby effects the movement of the automatic sear, and the consequent release of the hammer to automatically effect the firing of another round in the above described fashion. This form of operation continues automatically as long as the trigger is held in its rearmost position. Since the trip 170 is separate from the bolt, it does not reciprocate with the bolt, and it thereby provides the advantage that undesirable weight is not added to the recoiling members of the device and the weapon.

In the forward and backward movement of the bolt during operation, the bolt is well guided by the bent-in sections of the upper side of the tube 85, which as shown in FIG. 37 form guide ribs for the slots formed between the top of the bolt and the gas deflector. This guiding is accomplished with a minimum of friction, due to the small amount of contact area between the guide ribs of the tube and the slots formed at the top of the bolt.

While the invention has been described in detail with reference to a specific embodiment thereof adapted to be employed in combination with a particular conventional, it will be obvious that many variations and modifications may be made therein without departing from the spirit and scope of the invention, both with respect to use in the described weapon and for adapting the invention for use in other weapons, and it is therefore intended in the following claims to cover all such variations and modifications as may fall between the true spirit and scope of the invention.

Claims

What is claimed is:

1. A bolt assembly for converting a firearm for firing cartridges of a first caliber to the firing of cartridges of a second caliber by merely replacing the bolt of the firearm, wherein the firearm is of the type having a receiver, said assembly comprising a tube of resilient material having a flattened side and being insertable in the receiver, a first longitudinal slot in said flattened side extending substantially the length of said tube, the edges of said slot forming a bolt guide, a bolt slidably positioned in said tube and having a projection extending through said slot, plate means on said projection external of said tube, said bolt and plate means forming a pair of opposed slots guided by said bolt guide, a second longitudinal slot in the side of said tube opposite said flattened side and extending substantially the length of said tube, a back plate affixed in one end of said tube, whereby said tube forms a U-shaped spring, a chamber barrel member, means for releasably holding said chamber barrel member in the other end of said tube, said chamber barrel comprising means for receiving cartridges of the second caliber, said assembly being adapted for fitting into the receiver of the firearm.

2. The bolt assembly of claim 1 in which said tube has a plurality of transverse holes in the other end thereof, and said releasable holding means for said chamber barrel member comprises a plurality of lug means on said chamber barrel member positioned to engage said apertures, whereby said chamber barrel member may be assembled and disassembled by spreading apart the sides of said tube.

3. The bolt assembly of claim 1 wherein said bolt has a longitudinally extending firing pin slot aligned with said first slot in said tube, and said plate means covers the external side of said firing pin slot.

4. The bolt assembly of claim 1 wherein said bolt has a longitudinally extending ejector slot in a side thereof opposite said first longitudinal slot of said tube, said tube having a transverse slot adjacent said second longitudinal slot therein, and wherein said bolt assembly further comprises an ejector mounted in said transverse slot and having an ejector blade slidably extending into said ejector slot.

5. The bolt assembly of claim 4 wherein the edges of said transverse slot form knife edges, and the sides of said ejector are shaped to conform to said knife edges for holding said ejector rigidly in said tube, whereby said ejector may be assembled and disassembled in said tube by the spreading of said other end of said tube.

6. The bolt assembly of claim 1 further comprising a trip slidably positioned in said tube between one surface of said bolt and the inside surface of said tube adjacent said second longitudinal slot, said trip having a central aperture, said bolt having a projection extending into said central aperture for engaging one edge of said aperture upon movement of said bolt toward said chamber barrel member at a predetermined position.

7. The bolt assembly of claim 1 wherein said bolt has a longitudinally extending bore, and said assembly further comprises recoil spring means extending from said back plate into said bore, said bore having a shoulder engaging said spring for urging said bolt toward said chamber barrel member.

8. The bolt assembly of claim 1 wherein said plate means further comprises a transversely extending gas deflecting projection.

9. A bolt assembly for converting a firearm fireable in automatic and semi-automatic modes for firing cartridges of a first caliber to the firing of cartridges of a second caliber by merely replacing the bolt of the firearm, wherein the firearm is of the type having a receiver, said assembly comprising an elongated tube of resilient material having a pair of opposed slots longitudinally extending substantially the entire length of said tube, back plate means at one end of said tube, whereby said tube forms a U-shaped spring the other end of which may be sprung apart, a chamber barrel member, means releasable upon the spreading apart of said other end of said tube for releasably holding said chamber barrel member in said other end of said tube, and bolt means slidably mounted within said tube, said chamber barrel comprising means for receiving cartridges of the second caliber, said assembly being adapted for fitting into the receiver of the firearm.

10. The bolt assembly of claim 9 wherein said elongated tube has a plurality of apertures in the other end thereof, and said means releasably holding said chamber barrel member comprises lug means on said chamber barrel member positioned to engage said apertures.

11. The bolt assembly of claim 9 wherein the end of said chamber barrel member extending from said tube has the shape of a cartridge casing of a first caliber, and said chamber barrel member has an inner bore shaped to conform to a cartridge of a second caliber.

12. The bolt assembly of claim 9 wherein said bolt means has two generally D-shaped side portions engaging the inside of said tube, a bridge member joining said side portions and having an extension extending through one of said longitudinally extending slots in said tube, a longitudinally extending firing pin slot in said bridge member extending through said projection, and gas deflecting plate means externally of said tube and covering said firing pin slot, whereby said gas deflector and bolt means form a pair of opposed slots guided by the sides of said one slot of said tube, and a firing pin in said firing pin slot.

13. The bolt assembly of claim 12 wherein said D-shaped sides of said bolt means extend further in the direction away from said chamber barrel than said bridge, and wherein said firing pin is mounted to permit movement into the space between said D-shaphed sides beyond said bridge to permit engagement therein with a hammer.

14. The bolt assembly of claim 12 wherein said bolt means further has a longitudinally extending ejector slot on the side thereof toward the other longitudinally extending slot of said tube, said tube further having a transverse slot adjacent said other slot therein, and said bolt assembly further comprises an ejector member releasably clamped between the edges of said transverse slot and having an ejector blade slidably extending into said ejector slot of said bolt means.

15. The bolt assembly of claim 12 further comprising a recoil spring bore longitudinally extending in one of said D-shaped sides of said bolt means, and wherein said bolt assembly further comprises a recoil spring assembly extending from said back plate and into said bore for urging said bolt means toward said chamber barrel.

16. The bolt assembly of claim 12 further comprising a trip member slidably positioned in said tube between said bolt means and the inside of said tube adjacent to the other of said longitudinally extending slots in said tube, said trip means having a central aperture, a projection on said bolt means extending into said aperture in said trip means for engaging one edge thereof upon movement of said bolt to a position at a predetermined distance from said chamber barrel.

17. The bolt assembly of claim 16 further comprising an ejector slot in said bolt means, and ejector means fixedly mounted to said tube and having ejector blade means extending slidably into said ejector slot, said ejector being positioned to form a stop for said trip means in the direction toward said chamber barrel.

18. A bolt assembly for a firearm comprising a tubular member having a pair of opposed longitudinally extending slots and plate means closing one end of said tubular member, said tubular member being of a resilient material whereby said tubular member forms a U-shaped spring, bolt means slidably mounted within said tubular member, a transverse slot in said tubular member at one of said longitudinal slots, the edges of said transverse slot having knife edges, and an ejector member mounted in said transverse slot and having recesses that mate with said knife edges for holding said ejector in said transverse slot, said ejector having an ejector blade means extending into said tubular member and positioned in cooperative relationship with said bolt for the ejection of cartridge cases from said tubular member.

19. A bolt assembly for converting a firearm for firing cartridges of a first caliber to the firing of cartridges of a second caliber by merely replacing the bolt of the firearm, wherein the firearm is of the type having an automatic sear, said bolt assembly comprising a tubular member having a longitudinal slot extending substantially the entire length of said member, a bolt slidably mounted within said tubular member, a trip member slidably mounted in said tubular member adjacent said slot, said trip member having a rectangular recess adjacent said slot with one end of said recess forming automatic sear engaging means, said bolt having a projection extending into said rectangular recess for engaging the other end of said recess at a predetermined position of said bolt, said assembly being adapted for fitting into the receiver of the firearm.

20. A bolt assembly for converting a firearm for firing cartridges of a first caliber to the firing of cartridges of a second caliber by merely replacing the bolt of the firearm, wherein the firearm is of the type having a receiver, an automatic sear extending into said receiver and operatively coupled to a hammer, and a charging handle extending in said receiver and having a bolt engaging projection, said bolt assembly comprising a tube having a first longitudinal slot extending substantially the entire length of said tube and forming an opening into which the automatic sear and hammer may operatively extend, a second opposed longitudinal slot in said tube extending substantially the entire length of said tube, means connecting one end of said tube to constitute the same as a U-shaped spring, said second longitudinal slot in said tube forming a bolt guide, a bolt slidably positioned in said tube and having a projection extending through said second slot, and plate means on said projection outside of said tube and positioned to operatively engage the bolt engaging projection of the charging handle, said assembly being adapted for fitting into the receiver of the firearm.

21. The bolt assembly of claim 20 further comprising a back plate in one end of said tube, said bolt having a longitudinally extending bore, and recoil spring means in said tube extending from said back plate into said recoil spring bore for urging said bolt toward the other end of said tube.

22. The bolt assembly of claim 21 wherein said back plate includes a projection extending beyond said tube for aligning said bolt assembly in said receiver.

23. The bolt assembly of claim 21 further comprising chamber barrel means, and means for releasably holding said chamber barrel means in the other end of said tube.

24. The bolt assembly of claim 23 wherein said tube is formed of a resilient material whereby the sides of the other end on opposite sides of said longitudinal slots may be sprung apart to permit assembly and disassembly of said bolt and chamber barrel through said other end.

25. The bolt assembly of claim 24 in which said tube has a plurality of transverse apertures in said other end, and said means for releasably holding said chamber barrel therein comprises lug means on said chamber barrel for engaging said apertures.

26. The bolt assembly of claim 24 in which said bolt has a pair of generally D-shaped side portions engaging the insides of said tube and the end of said bolt toward said chamber barrel being connected by a bridge, thereby providing a space between the other ends of said D-shaped sides into which said hammer operatively extends, said bridge having a longitudinally extending firing pin slot extending into said projection of said bolt and being covered by said plate means.

27. The bolt assembly of claim 26 wherein the side of said bolt facing said first slot of said tube is flat, further comprising a trip member slidably positioned in said tube between said flat side of said bolt and the inside surfaces of said tube, said trip having a rectangular recess with one edge thereof being positioned to engage said automatic sear, said bolt further having a projection extendinG into said rectangular recess for engaging an opposite edge of said recess at a predetermined point in the movement of said bolt toward said chamber barrel.

28. The bolt assembly of claim 27 wherein said bolt comprises a longitudinally extending ejector slot, and further comprising an ejector member fixedly mounted with respect to said tube and having an ejector blade slidably extending into said ejector slot.

29. The bolt assembly of claim 26 in which said tube has an ejection port, and said bolt has an extractor slot longitudinally extending therein, further comprising an extractor lever pivoted in said extractor slot for engaging the rim of a cartridge case for ejection through said port.

30. A bolt assembly for converting a firearm firable in automatic and semi-automatic modes for firing cartridges of a first caliber to the firing of cartridges of a second caliber by merely replacing the bolt and magazine of the firearm, wherein the firearm is of the type having a receiver, an automatic sear extending into said receiver and operatively coupled to a hammer, a charging handle extending into the receiver and having a bolt engaging projection, and a gas tube extending into the receiver for automatic and semi-automatic operation of the bolt, and wherein said firearm further includes a recoil spring and buffer at the rear of the receiver; said bolt assembly comprising a tube insertable in said receiver and having a fixed back plate for engaging the buffer and recoil spring assembly of the firearm, a cartridge barrel held in the other end of said tube and having an outer end portion in the shape of a cartridge of said first caliber and an inner bore of the shape of a cartridge of said second caliber, whereby the buffer and recoil spring assembly of said firearm urge said bolt assembly into the breach of said firearm, said tube having an upper slot and a lower slot, a bolt slidable within said tube and having a projection extending through said upper slot, gas deflector plate means externally of said tube and affixed to said projection for effecting the movement of said bolt away from said chamber barrel in response to firing gases ejected into said receiver from said gas tube, a recoil spring assembly in said tube for urging said bolt toward said chamber barrel, a trip slidably mounted in said tube under said bolt, said trip having a rectangular recess with one edge thereof positioned to engage said automatic sear, a projection on said bolt for engaging an opposite edge of said recess at a predetermined position in the movement of said bolt toward said chamber barrel, a slot in the end of said bolt away from said chamber barrel, whereby said hammer can move into said slot in said bolt, a firing pin slot extending longitudinally in said bolt, and a firing pin positioned therein and adapted to extend into said space.

31. The bolt assembly of claim 30 wherein said tube is of a resilient material and forms a U-shaped spring thereby permitting assembly of the internal components of said bolt assembly in said other end of said tube.