US3139799A

US3139799A - Action for semiautomatic firearms

Info

Publication number: US3139799A
Application number: US185114A
Authority: US
Inventors: Carl H Benson
Original assignee: OF Mossberg and Sons Inc
Current assignee: OF Mossberg and Sons Inc
Priority date: 1962-04-04
Filing date: 1962-04-04
Publication date: 1964-07-07
Anticipated expiration: 1981-07-07

Description

E M N, .WI F S E IN1/EN TOR. Carri /Z/ Be/fsm 2 Sheets-Sheet 1 als www; NWS.

ACTION FOR SEMIAUTOMATIC FIREARMS July 7, 1964 c. H. BENSON ACITION FOR SEMIAUTOMATIC FIREARMS www www ww zwm v wm w mmw mmw N INVENTOR. Cdl l ZZ en S071 BY M 54M.

f/S TToJ/mya tions for semiautomatic firearms. part of the expanding gases of the fired cartridge are bled olf from the barrel and used to operate a piston and ac- United States Patent O 3,139,799 ACTION FOR SEMIAUTOMATIC FIREARMS Carl H. Benson, New Haven, Conn., assignor to O. F.

Mossberg & Sons, Inc., New Haven, Conn., a corporation of Connecticut Filed Apr. 4, 1962, Ser. No. 185,114 6 Claims. (Cl. 89-197) The invention relates generally to firearms and, more particularly, to semiautomatic firearms in which a tired cartridge is ejected, the action is cocked and another cartridge is inserted into the chamber each time the trigger is pulled.

There has recently been developed a new .22 caliber cartridge. This cartridge is known as the .22 magnum cartridge and is longer and more powerful than any other cartridge of .22 caliber. As a result of the increased power of the new cartridge and certain other aspects of its construction, the design of a semiautomatic action that will accept and re the new cartridge presents problems which the prior art has not had to cope with before.

Prior known semiautomatic actions for the other .22 caliber cartridges had, for the most part, employed actions operated by the recoil of the fired cartridge. In this type of action the bolt is not locked but is held against the car tridge in the chamber only by the pressure of the return spring. The inertia of the bolt is increased by making the bolt heavier than is otherwise necessary so that by the time the bolt starts to move rearwardly to open the breech the peak gas pressure created by the firing of the cartridge has passed. Thereafter the bolt is blown backwardly by the residue of expanding gasses and ejects the spent cartridge and cocks the action. When the gas pressure has dissipated the bolt returns under the pressure of the return spring and, in doing so, inserts a new cartridge in the chamber.

The new .22 magnum rim-lire cartridge, because it is much more powerful than previous .22 caliber rim-lire cartridges, does not lend itself for use with this customary type of semiautomatic action. One difliculty is that the gas pressures developed by the cartridge are so high that Weight of the bolt must be made very heavy if it is to hold the breech closed during the iirst few split seconds when peak cartridge gas pressures are being developed. While it has been possible in the case of other .22 caliber cartridges to make the bolt heavy enough without making the gun excessively heavy and without unduly impairing the handling ease of the firearm, it has been found that this is not the case with the .22 magnum rim-fire cartridge.

`The Weight of the bolt required to hold the breech closed against the higher gas pressures of this .22 magnum is so great as to adversely affect both the over-all weight of the gun and the ease with which it can be handled.

Another difficulty in employing this type of semi-automatic recoil action for the .22 magnum is the lack of a positive locking of the cartridge in the chamber. The .22 magnum, for which the present action has been designed, is a rim-fire cartridge as opposed to center-fire cartridges which have a heavier and stronger case. Due to the high gas pressures which the .22 magnum rim-lire ammunition develops, it must be locked tightly into the chamber by the bolt. If there is so much as a few thousandths of an inch clearance between the face of the bolt and 'the cartridge, the cartridge case is apt to rupture upon firing. Since the bolt is held against the cartridge only by spring pressure, the possibility of such clearance between the bolt and cartridge .cannot be ruled out.

Heretofore, the art has also employed gas-operated ac- In this type of action Patented July 7., 1964 ice tion bar that retract the bolt and cock the action. The piston Works against a return spring pressure which moves the bolt forwardly again to chamber the next cartridge after the gases from the fired cartridge are fully expanded.

This type of action has also been found to be unsuitable for use with the .22 magnum rim-lire cartridge. It is usually used on calibers greater than .22 or with .22 caliber center-fire ammunition, because fairly high gas pressures are required. Due to the necessity of keeping the magnum rim-fire cartridge locked up tight to prevent rupture, it was found impracticable to utilize gas from the barrel because the gas pressures available after it had become safe to unlock the breech were either not adequate or the point in time at which they were adequate was so close to the necessary lock-up time as to be too highly critical for a dependable action.

It was, thus, found that the two principal types of semiautomatic actions heretofore used in the art were unsuitable for use with the new .22 magnum rim-lire cartridge.

Accordingly, it is a general object of the invention to provide a novel semiautomatic action that will be satisfactory for use with the .22 magnum rim-lire cartridge.

More specifically, the invention has for its object the provision of an action for a semiautomatic firearm of .22 magnum rim-lire cartridge that will positively and tightly lock the cartridge in the chamber. Another object of the invention is to provide such an action that will be simple in construction and relatively inexpensive to manufacture. Still another object of the invention is to provide a semiautomatic action that is safe for use by relatively inexperienced shooters who customarily start out with weapons of .22 caliber.

Briey, and in general, the invention comprises an action in which the bolt is adapted to be cammed into a non-axial locking position as it completes the insertion of a new cartridge into the chamber. Camming of the bolt is effected by a bolt-operating member that follows behind the slides with the bolt in the receiver under the urging of a return spring. The bolt-operating member is provided with an inclined cam face that engages a similar cam face on the bolt when the bolt has reached the end of its forward travel to cam the rearward end of the bolt downwardly into a locking slot formed in the receiver. A second inclined cam face on the rearward end of the bolt then engages a correspondingly inclined surface at the back of the slot to lock the bolt tightly against the cartridge in the chamber.

The angles on the bolt and on the locking slot are carefully selected at values which will hold the bolt in battery position until it is safe to unlock the cartridgein the breech, that is, until the pressure of the gases from the fired cartridge are below a value that will burst the cartridge case. The bolt then slips upwardly out of the slot andthe remaining gas pressure from the fired cartridge is employed to retract the bolt, eject the spent cartridge and cock the action. Thereafter the return spring advances the bolt to chamber the next cartridge and then causes the bolt-operating member to cam the bolt into a locking position in the slot in the receiver.

For the purpose of illustrating one manner in which the invention may be made and practiced a presently preferred embodiment thereof is shown in the accompanying drawings and is described in detail hereinafter. But it is to be understood that the drawings and the detailed description to follow are by way of example only and do not define or limit the scope of the invention; the claims appended hereto, with their lawful equivalents, being relied upon for that purpose.

In the drawings:

FIG. 1 is a side elevation of a riiie embodying the invention;

FIG. 2 is an exploded perspective view of the bolt, boltoperating member and firing pin of the rifle shown in FIG. l;

FIG. 3 is an enlarged longitudinal sectional view through the receiver and fore-end of the rifle. shown in FIG. l showing the action in the process of inserting a new cartridge into the chamber;

FIG. 4 is a view similar to FIG. 3 showing the bolt locked in battery position;

FIG. 5 is a view similar to that of FIG. 3 showing the parts of the action shortly after the firing of the cartridge in the chamber; and

FIG. 6 is another similar longitudinal section showing the action cocked at the end of the bolt-retracting stroke.

While the invention will be explained with reference to its application to the .22 caliber magnum semiautomatic rifle shown in FIG. l, it will be readily appreciated by those in the art that the invention may be utilized in other types and calibers of firearms just a's well.

As is seen from FIG. l, the rifle shown there has a rear stock 10 and a fore-end 12. A barrel 14 and a receiver 16 are fitted to the foreend 12 in a cavity formed therein and are held in place by a mounting screw 17. At the underside of the fore-end 12 there extends a trigger 18 and trigger guard 20 as well as a cartridge magazine 22 which carries a number of cartridges that are constantly urged. upwardly toward the receiver under spring pressure. An ejection port 26 for spent cartridges is provided in the right side of the receiver 16 and the iired cartridges are ejected through this port on the backward stroke of the action. A laterally-extending bolt retracting stud 28 that may be manually drawn rearwardly in a longitudinal slot 30 formed in the receiver 16 is also provided at the right side of the rifle for manual operation of the action.

As is customary, a cartridge chamber 32 is formed in the rearward end of the barrel 14 and the rearward end of Ithe barrel is screwed into the front end of the receiver 16. The receiver is generally tubular in shape and has an internal cavity or bore 34 throughout its length that is coaxial with the breech chamber 32 in the barrel 1 4. It is one of the features of the invention that all of the major parts of the action are located within the bore 34 in the receiver 16. The rearward end of the receiver 16 is closed off by a threaded plug 36 that screws into the receiver. An extended head 38 is provided on the plug 36 and is so shaped to provide a smooth transition in line from the stock 10 to the receiver 16. p

Located in the bore 34 of the receiver 16 between the chamber 32 and the closure plug 36 are the major parts of the action; a bolt 40, a bolt-operating member 42 and a striker 44. The bolt 40 is formed with a generally cylindrical body portion 46 and has an arcuate recess 48 cut in the underside thereof to provide clearance for the cartridges in the magazine. A longitudinal groove 50 extends throughout the greater portion of one side of the bolt to permit the bolt to slide longitudinally past an ejecting bar 52 (see FIG. V6) positioned in the left side of the bore 34 of the receiver 16. Another longitudinal groove r54 extends completely through the top of the bolt 40 to accommodate the tiring pin 56. As is customary, a circular recess 58 is provided at the front face of the bolt 40 and the rim of each cartridge ts into this recess during the chambering `and ejection operations.

The bolt 40 is also provided with an extractor 60 that is positioned in Ia longitudinal groove formed in the right side of the body portion 46. The forward end of vthe extractor 60 terminates in an inwardly extending hook portion 62 that overlies the periphery of the 'circular recess '58. When a cartridge is seated in the recess 58, the hook portion 62 of the extractor 60 extends inwardly of the inner surface of the rim of the cartridge so that rearward movement of the bolt 40 and the extractor 60 causes 'the hook portion 62 to engage the cartridge rim and to withdraw the cartridge from the chamber 32 in the barrel 14. At its rearward end, the bolt has a pair of flat surfaces milled in its sides. The two vertical and

parallel ats

64, 64 thus formed iit between a pair of

arms

66, 66 formed on the bolt-operating member 42 which is disposed in the bore of the receiver right behind the bolt. Upper and lower inclined faces 69 and 71 respectively, are formed at the rearward end of the bolt and serve to cam and lock the bolt in battery position as described more fully hereinafter.

The bolt-operating member 42 has a cylindrical body portion 68 and a relatively long rod 70 extending rearwardly of the body portion 68. At its forward end the body portion has been cut away to form a large vertical slot 72 between the

arms

66, 66 that receive the bolt 40. The inner or rearward end 74 of the slot has been cut at an angle with respect to the vertical so that the face 74 of thev body portion 68 at that point is not vertical but is angled downwardly.

As in the case of the bolt 40, the bolt-operating member 42 has a longitudinal groove 76 formed in the top thereof to accommodate the firing pin 56. A short projection 78 is formed in the bottom of the groove 76 for the purpose of limiting longitudinal movement of the firing pin 56 in a manner to be described hereinafter. The bolt-operating member 42 also has a circular opening 80 extending transversely thereof to receive the inner end of the bolt retracting stud 28. The location of the opening 80 is such that the upper central portion is intercepted by the longitudinal groove 76 for the firing pin 56 and the bolt retracting stud 28, has, accordingly, a flat 82 on it (see FIG. 3) to provide clearance for the firing pin.

The bolt 40 and the bolt-operating member 42 are coupled together. Short, laterally-extending

pins

84, 84 are provided on the

flats

64, 64 on the rearward end of the bolt and these pins extend inwardly into a pair of

inclined slots

86, 86 formed in the

arms

66, 66 of the bolt-operating member 42. By reason of this arrangement, longitudinal movement of the bolt-operating member 42 serves to move the bolt 40 longitudinally in the bor'e 34 of the receiver 16.

A coil spring 88 is mounted on the extension rod 70 at the rear of the bolt-operating member 42 and one end of the spring 88 abuts against the rear face 90 'of the body portion 68 of the bolt-operating member 42 While the opposite end of the spring 88 fits against the bottom wall of a hollow tube 92 at the vfront of the bore closing plug 36. The spring 88 is always under a compressive stress and, as a result, constantly urges Ythe bolt-operating member 42 forwardly in the receiver bore 34.

Mounted rearwardly of the bolt-operating member v42 is the striker 44. The striker 44 is generally cylindrical in shape so as to conform to the bore 34 of the receiver 16 and adjacent its mid-portion has a section 94 of reduced diameter. The shoulder 96 formed at the change in diameter provides an engaging surface or 'sear notch for a sear 98 when the striker 44 is in its cocked position. Adjacent the front end of the striker the diameter tapers outwardly again to form a rst inclined surface or Yface 100. Just forwardly of the full diameter section 102 vthe striker 44 tapers inwardly to a reduced front end so as to form a second inclined face 104.

The striker is hollow, having a recess 106 that extends throughout almost the entire length thereof. The recess 106 in the striker accommodates a second coil spring 108 that is mounted around the outside of the hollow rtube 92 in the bore closure plug 36. One end of the spring abuts against the bottom wall 110 of the recess 106 while the opposite end abuts against the bottom wall of a vrecess (not shown) Vformed in the closure plug 36. Like the rst spring 88, the spring 108 is under a compressive stress and continuously seeks to relieve vstress by urging the striker 44 forwardly in lthe bore of the receiver. An access opening 112 in the bottoni wall 1'10 `of the recess 106 in the striker 44 serves to accommoansa/m date the rod-like extension 70 on the bolt-operating member 42 and this opening permits the striker to move longitudinally of the rod whenever possible.

As will be seen from reference to FIG. 2 a long, narrow tiring pin 56 is provided for the action and the liring pin fits within the

longitudinal slots

54, 76 formed in the tops of the bolt 40 and the bolt-operating member 42. The

sides

114, 114 of the forward end of the tiring pin 56 are milled away to form a narrow portion 116 for striking the rim of the cartridge and a notch 118 is formed in the underside of the rearward end of the tiring pin to fit over the short projection 78 at the bottom of the slot 76 in the bolt-operating member 42. When the tiring pin is positioned in the slot 76 the projection 78 extends upwardly into the notch 118 so that movement of the pin is limited by the engagement of the end walls of the notch with the projection. Movement of the firing pin occurs when the striker 44 strikes the rearward end of the tiring pin as described hereinafter.

Forward movement of the striker 44 against the tiring pin 56 is controlled by the sear 98. The sear 98, adjacent its mid-portion, is pivotally mounted on a pin 120 in the receiver 16 and has a rearwardly extending arm 122 and a forwardly extending arm 124. A leaf spring 126 is secured to the underside of the receiver by a screw 128 and extends forwardly thereof toengage the rearward arm 122 of the sear 98. The tension on the spring 126 is such that the engagement of spring with the sear tends to pivot the sear in a clockwise direction as viewed in FIGS. 3, 4, 5 and 6. Pivotal movement of the sear 98 in this direction moves the rearward arm 122 upwardly through a slot 130 into the bore 34 of the receiver 16. The end 132 of the rearward arm 122, accordingly, is shaped to form a point corresponding to the shape of the sear notch 96 on the striker so that it may serve as a sear catch.

A notch 134 is formed in the underside of the sear 98 just below the pin 120 and a channel shaped connector 136 normally abuts against the sear 98 at the notch 134. The connector 136 is slidably mounted in a U-shaped bracket 138 that is riveted to the underside `of the receiver 16. Mounting of the connector 136 in the bracket 138 is effected by a laterally-extending pin 140 that is secured to the

sides

142, 142 of the connector 136. The pin 140 extends beyond the

sides

142, 142 of the connector 136 and through

openings

144, 144 in the

side walls

146, 146 of the U-shaped bracket 138 that are elongated so as to permit a limited longitudinal movement of the connector relative to the bracket.

Longitudinal movement of the connector 136 is produced by a rearward pull on the trigger 18 that is pivotally mounted on a cross pin 148 in the

arms

146, 146 of the bracket 138. The lower portion of the trigger forms a curved linger piece 150 while the upper end of the trigger 18 has a notch 152 to receive the pin 140 extending through the connector 136. As the linger portion 150 of the trigger 18 is pulled rearwardly against the tension of a spring 154 wound around the triggers pivot pin 148 the notch 152 at the upper end of the trigger 18 moves the pin 140 longitudinally in the

elongated openings

144, 144 in the bracket 138. This also moves the connector 136 longitudinally of the bracket 138 and causes the sear 98 to pivot in a counterclockwise direction about its pivot pin 120. The connector 136 is constantly urged toward engagement with the sear 98 by the rearward end of the leaf spring 126 that lays across the top of the sides of the connector 136.

With the gun uncocked, the breech chamber 32 empty and a full cartridge magazine 22 in place, it is irst necessary to chamber the first cartridge 156 manually before the weapon may be fired serniautomatically. This is done by manually moving the bolt retracting stud 28 rearwardly in the slot 30 in the receiver 16. Inasmuch as the stud 28 extends inwardly into the bolt-operating member 42 this action moves the member 42 as well as the striker 44 rearwardly in the bore 34 of the receiver 16 against the pressure of the

springs

88 and 108. The bolt-operating member 42 moves but a very short distance before the

inclined slots

86, 86 in the

arms

66, 66 of the boltoperating member engage the

projections

64, 64 on the bolt 40. It will be realized that the bolt 40 will be in its locked position in which the lower inclined face 71 on the bolt is engaged with the rearward inclined face 158 on the locking slot 160 in the receiver 16. By reason of the angle of the

slots

86, 86 on the

arms

66, 66 of the bolt-operating member 42 further rearward movement of the member 42 lifts the bolt 40 out of its locked position. Thereafter the striker 44, bolt-operating member 42 and the bolt 40 all move rearwardly together.

As the striker 44 is moved rearwardly, the beveled rearward end surface 162 thereof contacts the sear catch 132 on the sear 98 and depresses it downwardly in the opening in the receiver 16. When the sear notch 96 on the striker 44 passes the catch 132, the catch moves upwardly to engage the notch 96 because of the spring pressure onthe sear. This locks the striker 44 in a cocked position.

As the bolt 40 was unlocked and withdrawn the

cartridges

164, 164 in the magazine 22 were raised slightly by the magazine spring (not shown). Now as the bolt 40 and the bolt-operating member 42 are thrust forwardly by the spring 88, the forward end 58 of the bolt 40 engages the rim of the topmost cartridge 156, moves it out of the magazine 22 and chambers it in the breech 32. FIG. l shows the positions of the parts just prior to the completion of the chambering stroke.

During the forward chambering stroke the bolt 40 moves along the axis of the bore 34 of the receiver 16. When the cartridge 156 is fully chambered in the breech 32 the bolt 40 canont move forwardly any farther. As a result of the

angled cam face

69, 74 on the rearward end of the bolt 40 and the bolt-operating member 42, the bolt 40 is cammed downwardly into the slot 160 and into engagement with the rearward angled face .158 thereof. In this way the bolt 40 is locked in battery position. Since the bolt 40 when locked up is in a non-axial position with respect to the bore 34 of the receiver 16, the face of the cartridge receiving recess 58 at the front of the bolt is angled so that it is square with the cartridge 156 when the bolt is in the battery position.

With the action in the battery position the rearward end 166 of the firing pin 56 extends slightly beyond the rearward face 90 of the bolt-operating member 42 ready to be struck by the striker 44. The finger portion of the trigger 18 is pulled rearwardly to cause the connector 136 to move forwardly and release the sear 98 from the sear notch 96 on the striker 44. Thereupon the striker 44 moves forwardly under the pressure of the sprnig 108 to strike the firing pin 56 which, in turn, lires the cartridge 156.

Within a few moments after the cartridge 156 is tired the gas pressures developed in the breech 32 reach a maximum and then begin to fall olf. These gas pressures tend to move the bolt 40 rearwardly but, because the bolt is locked against the angled face 158 at the rear of the slot in the receiver 16, cannot do so. However, the angle of the face 158 0f the slot and the corresponding inclined face 71 on the bolt are carefully selected to permit the bolt to slip upwardly after the peak gas pressures have been passed. The bolt 40 then slips upwardly into the receiver bore 34 and starts to move rearwardly. This opens the breech 32 but owing to the fact that the peak gas pressures have been passed, the opening of the breech does not result in the rupture of the cartridge.

The gas pressures, however, are sutiicient to move the bolt 40, the bolt-operating member 42 and the striker 44 rearwardly against the pressures of the

springs

88 and 108. As the bolt 40 moves rearwardly the extractor 62 on the bolt withdraws the fired cartridge from the chamber. A'his continues untilthe cartridge 156 strikes against the edge of the ejector 52 at the left side of the receiver bore 34 whereupon the cartridge istossed out the ejection port 26. Rearward movement of the action continues until the striker 44 is again locked in acocked position. The return spring 88 then moves the bolt-operating memf ber 42 and the bolt 40 forwardly to chamber a new cartridge in the breech.

`Care is taken to insure that one cartridge only is tired with each pull on the trigger. This is done by moving theconnector 136 out of the way of the pivotal sear 98 so that these-ar will not be blocked from engaging the Sear notch 96 on the striker. vAccordingly the connector 136 has an

upstanding portion

168, 168 on each side that extends upwardly into the bore of the receiver.v As the striker moves rearwardly these

upstanding portions

168, 168 are depressed by the first tapered face 100 at the front of the striker 44. This action moves the connector 136 out of engagement with the sear 98 at the time the Sear catch 132 is being pivoted upwardly into engagement with the sear notch y96 on the striker 44.

Thevaction also provides against firing the cartridge if Vthebolt 40 is not lockedup tight against the cartridge in the chamber. As will be seen in FIG. 4 the rearward end4 of Athe bolt-operating member 42 falls just in front of the end 170 of the forward arm 124 on the sear. If the bolt 40 is not locked up tightly the rearward end 90 of the member 42y would not lie forwardly of the arm 124. When the connector 136 tries to pivot the sear 98 ina counterclockwise direction the end I170 of the arm 124 will engage theend 90 of the bolt-operating member 42 to prevent withdrawal of the sear catch 132 from the scar notch 916.

VVhtV is claimed is:

l. An action for a semiautor'natic firearm, said action comprising `(ai) a barrel having a cartridge chamber formed in one end,

a receiver secured to the barrel, said receiver having an internal longitudinal cavity to accommodate the action and an inclined surface disposed v adjacent l'the cavity, v

('c) a bolt "in the receiver longitudinally reciprocable therein for ehambering and ejecting cartridges from the chamber in the barrel, said bolt having an inclined surface for engagement with the inclined surface on the receiver,

(d) a bolt-operating member in the receiverV rearwardly of the bolt and longitudinally reciprocable therein, said member having an inclined cam surface for camming' `the bolt intoy a positive chamber-locking position in which the inclined surface on the bolt engages rthe inclined surface on the receiver, (e) a firing pin 'passing through the bolt and the bolto'perating member, and v (f) a spring actuated striker in the receiver movable for engagement with the rearward end of the ring 2. An action for a semiautomatic firearm as set forth in claim l wherein the rearward end of the bolt is provided with two surfaces of Opposite inclination, the inclination of one of said surfaces corresponding to that of the inclinedy surface on the bolt-operating member whereby engagement of the said one surface with the inclined surface on the member cams the bolt laterally to `bring the other o-f'said two surfaces on the bolt into engagement with the inclined surface on the receiver.

3. An action for a semiautornatic fireman as 'set forth in claim 2 wherein the receiver is provided with a slot inthebottorn thereof and the rearward edge of said slot is beveled to form lthe inclined angle on the receiver.

4. Ari action for a semiauto-matic firearm as set forth in claim 3 wherein the underside of the bolt is partially cut away to define a downwardly extending lug that iits within the slot the receiver.

5. An action for a seniiautomatic firearm as set forth in claim 4 wherein the cavity in the receiver is cylindrical and the striker is longitudinally movable along the same axis as the bolt and bolteoperating member.

6 An action for a semiautomatic firearm as set forth in claim 5 wherein the bolt-operating member has a rearwardly extending rod and the striker is hollow and has a central opening to accommodate the rod on the member and wherein a closure is provided for the cavity in the receiver and two springs are mounted on the closure; one spring bearing against the inside of the hol'- l'ow striker to constantly urge the striker forward and the -o ther spring passing through the opening in the striker and bearing against the bolt operating member to constantly urge the member forward.

i References Cited in the file of this patent I FOREIGN PATENTS 631,038 Great Britain Oct. 26, 1949

Claims

1. AN ACTION FOR A SEMIAUTOMATIC FIREARM, SAID ACTION COMPRISING (A) A BARREL HAVING A CARTRIDGE CHAMBER FORMED IN ONE END, (B) A RECEIVER SECURED TO THE BARREL, SAID RECEIVER HAVING AN INTERNAL LONGITUDINAL CAVITY TO ACCOMMODATE THE ACTION AND AN INCLINED SURFACE DISPOSED ADJACENT THE CAVITY, (C) A BOLT IN THE RECEIVER LONGITUDINALLY RECIPROCABLE THEREIN FOR CHAMBERING AND EJECTING CARTRIDGES FROM THE CHAMBER IN THE BARREL, SAID BOLT HAVING AN INCLINED SURFACE FOR ENGAGEMENT WITH THE INCLINED SURFACE ON THE RECEIVER, (D) A BOLT-OPERATING MEMBER IN THE RECEIVER REARWARDLY OF THE BOLT AND LONGITUDINALLY RECIPROCABLE THEREIN, SAID MEMBER HAVING AN INCLINED CAM SURFACE FOR CAMMING THE BOLT INTO POSITIVE CHAMBER-LOCKING POSITION IN WHICH THE INCLINED SURFACE ON THE BOLT ENGAGES THE INCLINED SURFACE ON THE RECEIVER, (E) A FIRING PIN PASSING THROUGH THE BOLT AND THE BOLTOPERATING MEMBER, AND (F) A SPRING ACTUATED STRIKER IN THE RECEIVER MOVABLE FOR ENGAGEMENT WITH THE REARWARD END OF THE FIRING PIN.