US3274724A

US3274724A - Rifle bolt mechanism

Info

Publication number: US3274724A
Application number: US459990A
Authority: US
Inventors: John H Brandt
Original assignee: Individual
Current assignee: Individual
Priority date: 1965-06-01
Filing date: 1965-06-01
Publication date: 1966-09-27
Anticipated expiration: 1983-09-27

Description

Sept. 27, 1966 J, H, BRANDT RIFLE BOLT MECHANISM 2 Sheets-Sheet l Filed June l, 1965 mm. mh mm.

Sw Nm E ATTORNEY @pt 27, w66 J. H. BRANDT 3,274,724

RIFLE BOLT MECHANISM Filed June l, 1965 2 Sheets-Sheerl 2 zNvENToR John H. Bmnd ATTORNEY United States Patent O 3,274,724 RIFLE BOLT MECHANISM John H. Brandt, Irving, Tex. (2120 Irving Blvd., Dallas, Tex. 75207) Filed .lune 1, 1965, Ser. No. 459,990 9 Claims. (Cl. 42-16) This invention relates to rifle bolt mechanisms, and more particularly to a rifle bolt mechanism of the manually operated type having an improved construction for maximum strength, ease of operation and minimum of wear; and yet of a simplified design for economy of manufacture.

The broad object of this invention may be stated as the provision Aof a rifle -bolt action of the -manually operated type which is designed for overall simplicity of construction for economy of manufacture, consistent with a construction which gives a maximum strength for safety when the bolt is locked, is operable with maximum ease and is characterized by a minimum of wear during use. To accomplish this purpose, the bolt comprising the main body of the action is more generally symmetrical and smooth along its length and incorpor-ates a plurality of integral front end locking lugs disposed symmetrically about the periphery thereof, wherein a maximum locking lug area is utilized to give maximum strength while using enough locking lugs to reduce the angle the bolt must be rotated between the locked and unlocked positions. A tiring pin is housed within the bolt and is actuated simultaneous with and responsive to the unlocking of the bolt by means of a plurality of cams and cam followers spaced symmetrically about the axis -of the firing pin to eliminate any lateral torque being exerted on the pin and to insure cocking force exerted only along this axis. A ball is utilized to act as the engaging means between the cocking piece connected to the ring pin and the trigger mechanism so as to eliminate frictional wear inherent in more conventional sear engagements and to provide a much smoother release of the firing pin.

Other objects, features and advantages will become readily apparent from the following detailed description of the preferred embodiment of the invention when taken in conjunction with the appended claims and the attached drawing wherein like reference numerals refer to like parts throughout the several g'ures, and in which:

FIGURE l is a side elevational view in section of the lrifle bolt mechanism of the invention;

FIGURES 2A and 2B are elevational views in section taken through section line 2 2 of FIGURE 1 showing, respectively, the locking mechanism of the bolt and receiver when in the locked and unlocked positions;

FIGURE 3 is a fragmentary plan view of the rear section of the bolt illustrating a pair of diametrically opposed cam surfaces within which ride, respectively, a pair of cam followers attached to the cocking piece;

FIGURE 4 is a side elevational View in section of the bolt sleeve which houses the cocking piece;

FIGURE '5 is a perspective view of the cocking piece which attaches to the firing pin;

FIGURE 6 is a side elevational view in section of the cocking piece shown in FIGURE FIGURE 7 is a fragmentary plan view, partly in section, of the rear section of the -bolt and tiring pin, additionally showing the cocking piece and the bolt sleeve, wherein the firing pin and cocking piece are in the red position;

FIGURE 8 is an elevational view in section taken through section line 8 8 of FIGURE 1 showing the assembly of the cocking piece within the bolt sleeve;

FIGURE 9 is an elevational View in section taken through section line 9 9 of FIGURE 1 showing the position of the cam followers when engaging the cam surfaces at the rear of the bolt; and

FIGURE l0 is a fragmentary plan View, partly in section, of the rear portion of the `bolt and firing pin, additionally showing the cocking piece and bolt sleeve, when the tiring pin is in its cocked position.

Referring now to FIGURE 1, which is an elevational view in section of the bolt mechanism of the invention, the mechanism comprises a receiver 20 which attaches to the rear of the barrel of a rille (not shown), a bolt 22 slidably engaged within a bore 23 of circular cross section within the receiver, a firing pin 24 disposed within a bore or channel 50 within the bolt, a cocking piece 26 secured by threads to the rear end of the firing pin, and a bolt sleeve 28 in threaded engagement with the rear of the bolt and enclosing the cocking piece. The receiver includes an interior threaded portion 34 extending beyond the front of the bolt which screws onto the rear end of a conventional barrel. The receiver also includes locking lugs 36 extending inward from the wall of the receiver channel 23 which engage similar locking lugs 46 provided on the bolt. When in the locked position, the locking lugs 46 integral with the bolt are disposed in the front of the receiver locking lugs, wherein the channel 38 Within which the bolt locking lugs are disposed is the same diameter as the channel 23 running the major length of the receiver. An opening 40 is cut out of the receiver for loading and ejecting cartridges when the bolt is withdrawn,

The bolt comprises an elongated section of substantially constant outside diameter just slightly less than the inside diameter of channel 23 -of the receiver, a length of restricted diameter 44 which passes between the locking lugs 36 of the receiver, and locking lugs 46 disposed in front of the receiver locking lugs when the `bolt is positioned to its most forward position, wherein the bolt locking lugs 46 have an outside diameter equal to the outside diameter of the elongated section `of the bolt. There are three bolt locking lugs 46 symmetrically disposed about the end of the bolt, the periphery of each of which defines an arc of a circle subtending an angle of slightly less than 60 taken from the center line of the bolt, so that the spacial separation between adjacent bolt locking lugs subtends an angle slightly in excess of 60. Similarly, there are three complementary receiver locking lugs equally spaced about the inside surface of the receiver, wherein each receiver locking lug subtends an angle of 60 taken from the center line of the receiver, so that the spacial separation between adjacent receiver locking lugs subtends an angle of 60. When the bolt is rotated 60 by a bolt handle, the bolt locking lugs are rotated to a position coinciding with the spaces between the receiver locking lugs. In this 'unlocked position, the bolt can then be withdrawn, whereas the bolt is locked in place for firing when the bolt locking lugs coincide with the receiver locking lugs. The bolt can be more clearly seen in its locked position in FIGURE 2A, which is an elevational view in section taken through section lines 2 2 of FIG- URE l; the bolt is shown more clearly in its unlocked position in the elevational view in section of FIGURE 2B, also taken through section lines 2 2 of FIGURE l, wherein the bolt lugs`are disposed to coincide with the spaces between the receiver locking lugs. Because of this particular construction, it will 'be seen that a maximum locking lug surface area is utilized for locking the bolt in place in the firing position to provide maximum safety and strength when the bolt is locked. This is due to the fact that the total area of each the bolt and receiver locking lugs is maximized with only enough space between adjacent locking lugs to permit the bolt to be withdrawn. Thus this condition is achieved when the total tarea of either the 'bolt or receiver locking lugs, or the total angle subtended thereby, is equal to the total area of the spaces Patented Sept. 27, 1966 i between the locking lugs, or the total angle subtended by these spaces, respectively. It will be noted that the receiver locking lugs project from the interior wall of the receiver channel, and that the bolt includes a length 44 of restricted diameter to pass between these lugs and bolt locking lugs of outside diameter equal to the diameter of the bolt, so that the major length of the receiver channel can be made of uniform diameter. This eliminates the necessity of machining grooves within the receiver channel wall for the passage of bolt locking lugs therein as is the case in more conventional fire arms wherein the bolt locking lugs project beyond the diameter of the bolt itself.

The bolt defines a channel 50 formed therein along its axis for containing a firing pin 24, which channel includes a length 52 of restricted diameter at the front of the bolt terminating at one end in the larger diameter portion of the channel with an annular shoulder 54 and at the other end within the front wall 58 of the bolt. This front wall defines .a small circular hole 59 through which the point 60 of the firing pin can project and a cartridge containing recess 56 defined by an annular projection 57 on the front wall concentric with hole 59. The firing pin 24 is disposed within the bolt channel 50 and has an outside diameter less the inside diameter of the bolt channel, so that a firing pin spring 25 can be positioned about the firing pin between the outside diameter thereof and the wall of the bolt Channel. The firing pin has an enlarged annular shoulder portion 61 of outside diameter equal to the inside diameter of the bolt channel and abuts against shoulder 54 when the firing pin is in its most forward position. The ring pin also includes a length 62 of reduced diameter which projects beyond shoulder 61 into the reduced diameter length 52 of the bolt channel, and finally a length 63 of yet further restricted diameter which defines the firing point 60 at the front end thereof that projects through hole 60 beyond the front wall 58 of the bolt.

Referring now to both FIGURE l and the fragmentary top plan view, partly in phantom, of FIGURE 3, the bolt channel includes a threaded length 64 adjacent to but spaced from the rear thereof into which the bolt sleeve 26 is screwed, and a length 66 of enlarged inner diameter between the threaded length 64 and the rear wall 76 of the bolt. Defined in the top of the bolt is Ia cam surface 68 which is cut through the wall of the bolt to communicate with the enlarged diameter length 66. This cam surface includes a surface 69 perpendicular to `the rear wall 76 of the bolt and a gently curving surface 70 defined between the rear wall of the bolt and the perpendicular wall 69k along which a cam follower can ride. Diametrically opposite to cam surface 68 is another cam surface 72 formed in the bottom of the bolt which includes a surface 73 perpendicular to the rear wall 76 of the bolt and a gently curving surface 74 between the wall 73 and wall 76. This cam surface is identical but perverted to cam surface 68. As will be shown later, corresponding cam followers integral with the cocking piece ride on the cam surfaces to cock the firing pin when the bolt is manually rotated from its locked to its unlocked position. The reason for two cam surfaces which Iare disposed diametrically opposite to each other is yto ensure that no lateral torque or bending moment is exerted on the firing pin when it is cocked. By providing the diametrically opposed cam surfaces and followers, the firing pin is withdrawn directly backwards with a force exerted exactly along its axis, thus greatly reducing wear on the firing pin itself. Also of major importance is the fact that two dual, opposing cams enable the firing pin mechanism to be cocked with much greater ease and less force than in conventional bolt actions.

A bolt sleeve 28, which houses the cocking piece 26, is Ithreadedly engaged with the threaded interior length 64 of the bolt. A side elevational View in section of the bolt sleeve is shown in FIGURE 4 and includes a cylindrical length which has an outside diameter equal to the nside diameter of the enlarged bolt channel length 66 and projects therein. Integral with and projecting beyond the cylindrical length 80 is a threaded length 82 which threads into the threaded length 64 of the bolt channel. When these two pieces are screwed together, the rear wall 76 of the bolt is adjacent to wall 84 of the bolt sleeve, the latter of which is an integral part of the cylindrical length 80 and the main body of the bolt sleeve. In other words, the wall of the bolt fits within an annular channel 85 between the outer wall 88 and the cylindrical length 80 of the bolt sleeve. A circular channel 86 is defined through the

sections

80, 82 of the bolt sleeve along the axis thereof through which the rear portion 120 of the firing pin passes, to be described below. A front shoulder 89 is defined on the outer wall 88 of the bolt sleeve which abuts against the bolt handle when the bolt and bolt sleeve are engaged, and a hollow interior 90 which is open at the bottom is defined within the main body of the bolt sleeve to house the cocking piece. It should be noted that the bolt sleeve is a single integral piece. As will be shown more clearly in the following figures and description, diametrically opposed slots 91 and 91a are provided in the wall 84 and cylindrical length 80 of the bolt sleeve for the passage therethrough of the cam followers of the cocking piece which engage the cam surfaces provided in the rear of the bolt, whereas only the circular hole 86 is defined in the threaded length 82.

A perspective view of the cocking piece is shown in FIGURE 5 and comprises a pair of diametrically opposed cam followers and 102 aligned in a vertical plane having rounded

front surfaces

101 and 103, respectively. The two cam followers are separated by a threaded circular channel 104 through which the threaded end of the firing pin passes and is threaded. The main body 106 of the cocking piece is wider than the cam followers and includes .a trigger mechanism engaging member 108 for holding the firing pin in a cocked position. A threaded hole 110 is also defined through the main body of the cocking piece aligned with the threaded circular channel 104. The cocking piece is fitted up into the recess 90 of the bolt sleeve 28 from the bottom thereof with the

cam followers

100 and 102 being positioned within the slots 91 and 91a.

After the cocking piece has been inserted in the bolt sleeve, the firing pin, with spring 25 assembled thereabout, is inserted through hole 86 of the bolt sleeve to be threadedly engaged with the cocking piece. The firing pin comprises a main body portion 24 terminating at its rear end in a reduced diameter length 120, the rearmost portion 122 of which is threaded to match the threads of the cocking piece. A side elevational view in section of the cocking piece is shown in FIGURE 6, wherein it can be more clearly seen that the interior edges of the

cam followers

100 and 102 are threaded along the channel 104, and that the channel or hole 110 continues throughout the main body portion of the cocking piece and is similarly threaded. The firing pin is threaded into this cocking piece and tightened, all this being shown in FIG- URE 1, wherein the firing pin is free to move relative to the bolt sleeve through hole 86 therein. In this assembled configuration, the firing pin spring 25 is retained between the front shoulder 61 of the firing pin and the front wall 87 of the bolt sleeve. Then, this assembly is threaded into the rear of the bolt by screwing together the threaded portions of lthe bolt sleeve and bolt with the firing pin extending into the bolt channel, all as shown in FIGURE 1.

Referring now to FIGURE 7, which is a fragmentary top view, partly in section, of the rear portion of the bolt mechanism, it will be seen that the forwardly extending

lengths

80, 82 of the bolt sleeve extends into the interior of the bolt and is in threaded engagement therewith, with the annular rearmost portion of the bolt extending back into the bolt sleeve within the annular channel 85 thereof. The threaded engagement between the bolt sleeve and the bolt is not completely tightened so that the bolt can be rotated by bolt handle 1-12 relative to the bolt sleeve. 'Dhus the rear wall 76 of the bolt does not fit tightly against wall 84 of the bolt sleeve but is adjacent thereto. It can also be seen that the restricted diameter length 120 of the ring p-in passes through hole 86y in the bolt sleeve and is threaded at 122 securely within the cooking piece 26. Moreover, this view shows the top cam follower 100 passing through slot 91 in wall 84 of the bolt sleeve and into cam surface 68 of the bolt. The curvature of lthe front edge 101 of the cam follower 100l is rounded to match the gently curving edge of the cam surface. This view represents the firing p-in in the fired position. The spring 25 terminates and abuts at the front end against shoulder 61 of the firing pin and at the rear end against front surface 8.7 of the bolt sleeve.

The slots 91 and 91a through the wall 84 of the bolt sleeve are shown more clearly in the elevational view in section of FIGURE 8 taken through section lines 8 8 of FIGURE l. Here it can be seen that the restricted diameter llength 122 of the ring pin is threaded through the channel 104 between the two cam followers and back into the cooking piece. Also apparent is the hole 86 in the fron-

t extension

80, 82 of the bolt sleeve through which the firing pin passes, and slots 91 and 91a dened in the upper and lower halves of forward extention 80 and the wall Y84 of the bolt sleeve through which the

cam followers

100 and 102 pass int-o the interior of the bolt sleeve. As shown, more cleanly in the elevational View in section of FIGURE 9, which is taken in the opposi-te direction through section lines 9-9 of FIGURE 1, the

cam followers

100 and 102 are positioned in the cam surfaces 68 `and 72, respectively, in the rear wall of the bolt. This View clearly shows the diametrically opposite placement of the cam surfaces and cam followers which results in a cocking force exactly aligned with the axis of the firing pin to eliminate any undesirable torque. Member 108 is integral with the cocking piece 26 and extends downward for engaging the trigger mechan-ism is seen in FIG- URE 8 to move back and forth in a channel 140 provided in the bottom of the receiver as the firing pin and/or bolt are moved back and for-th. The opposing sides of the bolt sleeve terminate at flat ends 130 and 1312 against

yhat shoulders

134 and 136` of the receiver, respectively, whereby the bolt sleeve rides back and forth on these receiver shoulders. As the bolt is rotated in either direction, it will be seen that the bolt sleeve is restrained from rotation as a result of the abutting relation between the bolt sleeve and receiver, thus allowing the ring pin to be cocked. A hole (not shown) is provided in the bottom of the receiver beneath member 108 within which a solid ball 150 is loosely housed, wherein the ball is the connection between the iring pin mechanism and the trigger mechanism, all as will be described below.

As shown in FIGURE 7, the bolt is in its locked position and the firing pin in its most forward position, or the red position. To eject a spent cartridge and cook the tiring pin, the bolt handle 112 is lifted upward approximately 60 to position the bolt locking lugs in correspondence with the spaces between the receiver locking lugs. In this position, the bolt can be withdrawn, as noted before. `In so lifting the bolt handle, the bolt is rotated relative to the bolt sleeve, the latter of which is restrained from rotational movement as will be shown below. This relative rotation between the bolt and the bolt sleeve is possible because of the loose threaded connection therebetween. As the bolt is rotated, the

cam followers

100 and 102 ride along the cam surfaces 70 and 74, respectively, `forcing the cocking piece directly backward. Because of the rigid connection be-tween the cocking piece and the firing pin, the tiring pin is therefore withdrawn. When the bolt handle is rotated upward by its maximum amount of about 60, the

front edges

101 and 103 of the cam followers are moved lbackward to correspond approximately with the rear wall 76 of the bolt, aill this being shown in the fragmentary plan View, partly in section, of FIGURE 10. This view shows the bolt rotated approximately 60 with the cam surfaces rotated accordingly. In this position with the cooking piece and tiring pin withdrawn, the spring 25 -is compressed between the shoulder 61 of the ring pin and the front edge 87 of the bolt sleeve. As will |be described in more detail later, the downward projecting member 108 integral with the cooking piece engages the trigger mechanism when the cocking piece -is forced rearward, wherein the trigger mechanism holds the firing pin in a cocked position until the trigger is pulled. After the bolt is rotated 60 to unlock it and cock the firing pin, the entire bolt assembly is withdrawn relative to the receiver 20 to eject the spent cartridge and reload. The bolt is then moved forward again and rotated back to lock the bolt in ring position, and the ring pin is still withdrawn after this movement until the trigger is pulle-d.

Referring again to FIGURE l, the trigger mechanism will now be described, wherein it wil-l be remembered that one of the objects of the invention is to provide an action which minimizes wear during operation, and permits 4a maximum ease of operation. As noted earlier, member 108 rides in channel 140 of the receiver, and beneath the member is defined a hole 149 in the receiver within which a ball 150y is housed for engaging the bottom of member 108. Directly beneath the ball and urging it upward is an arm piv-oted at one end about pivot l162 and engaging the bottom of the ball at the other end, whereby the arm is biased upward by spring 164. The ring pin is shown in FIGURE l in its tired position, and when tired, member 108 (including the cocking piece and firing pin) is in its most forward position. IIn this position, the member 10-8 rides up over the ball urging the ball downward and compressing spring 164. When the ring pin is cocked, member 108 is moved backward so that the slanted, front llower edge 109 bears against the ball 150, since arm 160 will urge the ball higher as the cocking piece is moved rearward. The ring pin will remain cocked as l-ong as the ball is held upward in this position, wherein the mechanism for so doing will now be described. l

An upright sear 166, integral with the trigger piece 165, is adapted to move under the lower front end of the arm 160 at its upper end when the bolt is rotated to cock the tiring pin. This action is provided by another arm integral with the trigger piece that is biased upward by a spring 172, with the entire trigger piece being pivoted on a suita-ble pivot 168. In otherwords, as the cocking piece is moved rearward to allow the ball to move upward in front thereof .as a result of arm 160 being moved upward, spring 172 acting against arm 170 will rotate sear 166 under arm 160. Once this occurs, ball 150 will be held in this position (thus maintaining the ring pin cocked) until sear 1.66 is rotated forward by some external force. The trigger 174 also forms an integral part of the trigger piece, and when urged backward, sear 166 is rotated forward to allow the ring pin spring 25 to re t-he pin, and thus urge bal-l 150 downward again. Suitable adjustments can be provided to govern the degree of movement of the firing piece for greater or less sens-itivity. Here, a sear engagement adjustment screw 176 is positioned behind the trigger piece above the pivot 168 to limit the amount by which the trigger piece can rotate counterclockwise, and thus lim-i-t the degree of engagement of sear 166 and arm 160. An overtravel adjustment screw 178 is also positioned behind the trigger below the pivot 168 to limit the degree of rotation of the trigger piece in a clockwise direction. Thus the trigger piece will abut these screws, respectively, when it rotates in opposite direction.

Because of the ball 150 providing the almost frictionless engagement between the cooking piece and trigger mechanism, there is very little wear during operation of the action, and a very smooth trigger and firing action results which, Iof course, yallows greater accuracy in ring. This is in contrast to a sear engaging the cocking piece that would result in more friction and rougher action.

Although the invention has been described with reference to a particular embodiment thereof, it will be understood by those skilled in the art lthat certain modications and substitutions thereof can be made that fall within the true scope of the invention, which invention is intended to be limited only as defined by the appended claims.

What is claimed is:

1. A rifie bolt mechanism comprising:

(a) a receiver member having a bolt channel therein adapted for being secured at the front end thereof to a barrel member and defining rst locking lug means adjacent said front end,

(b) a bolt member rotatably and slidably mounted in said bolt channel defining second locking lug means adjacent the front end thereof for engaging said first locking lug means in locking relation therewith when said bolt is rotated to its firing position,

(c) said bolt member defining a pair of diametrically opposed cam surfaces in the rear wall thereof,

(d) a firing pin ase'mbly mounted within said bolt member and extending from said rear wall thereof,

(e) a cocking piece adapted to engage a trigger mechanism securely attached to said firing pin assembly extending from said rear wall of said bolt member and defining a pair of diametrically opposed cams for engaging said pair of cam surfaces, respectively, for withdrawing said firing pin assembly and cocking piece to a cocked position relative to said bolt when said bolt is rotated from said firing position to an unlocked position, and

(f) a non-rotatable bolt sleeve member disposed about said cocking piece to prevent rotation of said cocking piece when said bolt is rotated.

2. A rifle bolt mechanism according to claim 1 wherein said bolt sleeve rides along said receiver member in non-rotating relation therewith.

3. A rie bolt mechanism according to claim 2 where in said bolt sleeve is in loosely threaded engagement with said bolt member for relative rotation therewith.

4. A rifle bolt mechanism according to claim 1 wherein said lcocking piece includes a downwardly extending member defining a slanted surface at the front thereof, including a ball disposed beneath said downwardly extending member in engagement therewith, first means for biasing said ball upward against the bottom of said downwardly extending member when said firing pin assembly and cocking piece are in the fired position and against said slanted surface when said firing pin assembly and cocking piece are in said cocked position and second means for engaging said first means when said firing pin assembly and said cocking piece are in said cocked position for releasably maintaining said ball against said slanted surface and said firing pin.

S. A rifle bolt mechanism according to claim 4 Wherein said ball is disposed within a hole in the bottom of said receiver, said first means comprises a pivoted lever and first resilient means biasing said lever upward, and said second means comprises a pivoted trigger piece including an upright sear for engaging the bottom of said lever, second resilient means biasing said trigger piece to rotate said sear in one direction under said lever, and a trigger for rotating said sear in an opposite direction.

6. A rifie bolt mechanism according to claim 1 wherein said first locking lug means comprises a first plurality of spaced apart locking lugs extending inwardly from the wall of said bolt channel and said second locking lug means comprises a second plurality of spaced apart locking lugs extending outwardly from the periphery of said bolt which engage said first plurality of locking lugs in front thereof, respectively, when said bolt is in said firing position and are adapted to pass through the spaces between said lirst plurality of locking lugs when said bolt is rotated from said firing position to said unlocked position.

7. A rifle bolt mechanism according to Claim 6 wherein said bolt defines a reduced diameter length adjacent the rear of said second plurality of locking lugs for passing between said rst plurality of locking lugs.

8. A rifie bolt mechanism according to claim 7 wherein the radii of said second plurality of locking lugs from the axis of said bolt are equal to the radius of the major portion of said bolt.

9. A rifle bolt mechanism according to claim 6 wherein said first and said second plurality of locking lugs are equally spaced about the wall of said bolt channel and said bolt periphery, and the total areas of each of said first and said second plurality of locking lugs are substantially equal to the total areas of the spaces between said frst and said second plurality of locking lugs, respectively.

No references cited.

BENJAMIN A. BORCHELT, Primary Examiner.

Claims

1. A RIFLE BOLT MECHANISM COMPRISING: (A) A RECEIVER MEMBER HAVING A BOLT CHANNEL THEREIN ADAPTED FOR BEING SECURED AT THE FRONT END THEREOF TO A BARREL MEMBER AND DEFINING FIRST LOCKING LUG MEANS ADJACENT SAID FRONT END, (B) A BOLT MEMBER ROTATABLY AND SLIDABLY MOUNTED IN SAID BOLT CHANNEL DEFINING SECOND LOCKING LUG MEANS ADJACENT THE FRONT END THEREOF FOR ENGAGING SAID FIRST LOCKING LUG MEANS IN LOCKING RELATION THEREWITH WHEN SAID BOLT IS ROTATED TO ITS FIRING POSITION, (C) SAID BOLT MEMBER DEFINING A PAIR OF DIAMETRICALLY OPPOSED CAM SURFACES IN THE REAR WALL THEREOF, (D) A FIRING PIN ASSEMBLY MOUNTED WITHIN SAID BOLT, MEMBER AND EXTENDING FROM SAID REAR WALL THEREOF,