US3895752A

US3895752A - Explosive powder driven setting gun with silencing device

Info

Publication number: US3895752A
Application number: US355666A
Authority: US
Inventors: Shigefumi Hatayama; Masao Tsunekawa
Original assignee: Hilti AG
Current assignee: Hilti AG
Priority date: 1972-05-02
Filing date: 1973-04-30
Publication date: 1975-07-22
Anticipated expiration: 1992-07-22
Also published as: BE798925A; FR2183000B1; FR2183000A1; AT333215B; ATA309573A; DE2221374C2; JPS4954979A; CA993151A; IT982655B; DE2221374A1; CH550643A; JPS5545353B2; GB1399776A

Abstract

In an explosive powder driven setting gun, the barrel is laterally enclosed by a sleeve and at least a portion of their juxtaposed surfaces are spaced apart forming an axially extending ring-shaped slot intermediate the ends of the barrel. At the end of the ring-shaped slot closer to the rearward end of the bore in the barrel, connecting passages communicate between the bore and the ring-shaped slot. Axially extending gas passages in the form of slots extend radially inwardly from the ring-shaped slot to the bore in the barrel. At the forward end of the barrel, outlet openings extend from the bore to the muzzle end of the barrel. Preferably, the outlet openings are grooves formed in the surface of the bore and they extend between the gas outlet passages and the muzzle end of the barrel so that the cross sectional area of the bore at the muzzle is increased. Gases generated within the bore when the setting gun is fired flow through the connecting passages into the ring-shaped slot where they change direction and pass through the gas outlet passages back into the bore and finally out of the barrel through the outlet openings at its muzzle end to afford a silencing effect.

Description

United States Patent H 1 [111 3,895,752

Hatayama et al. 7 1 July 22, 1975 EXPLOSIVE POWDER DRIVEN SETTING Primary Examiner-Granville Y. Custer, Jr

GUN WITH SILENCING DEVICE Attorney, Agent, or FirmToren, McGeady and Stanger [75] Inventors: Shigefumi Hatayama, Futtsu; Masao Tsunekawa, Sooka, both of Japan [57] ABSTRACT Assigneel F Aktien'gesellschafli In an explosive powder driven setting gun, the barrel is Llechlenstem laterally enclosed by a sleeve and at least a portion of [22] Filed: Apt 30, 1973 their juxtaposed surfaces are spaced apart forming an axially extending ring-shaped slot intermediate the [21] Apple N03 355,666 ends of the barrel. At the end of the ring-shaped slot closer to the rearward end of the bore in the barrel.

[30] Foreign A ii fi p m Data connecting passages communicate between the bore May 2 1972 Germany 222374 and the ring-shaped slot. Axially extending gas passages in the form of slots extend radially inwardly 52 US. Cl. 227/10 from bore the forward end of the barrel, outlet openings extend [5|] B25c 1/14 I 581 Field of Search 227/8, 9, 10, l i from the muzzle lbly, the outlet openings are grooves formed in the sur- [56] References Cited face of the bore and they extend between the gas out let passages and the muzzle end of the barrel so that UNITED STATES PATENTS the cross sectional area of the bore at the muzzle is in- 2,773,259 l2/l956 Broughton 6'! Bl r. 227/ll reased Gases generated within the bore when [he 2,775,762 1/1957 Hilti 227/ll setting gun is fired flow through the connecting pas- :Tl a sages into the ring-shaped slot where they change di- 3 407 982 10/1968 i I i I I i i I i 4 i I I I I i i i 227/9 rection and pass through the gas outlet passages back 3 658 229 4/1972 Pomeroy iiii it; IIIjlljIIIn/m the bore and finally out of the barrel through the outlet openings at its muzzle end to afford a Silencing effect.

7 Claims, 6 Drawing Figures Pmmimum ms 3. 895752 SHEET 1 FIG.1

PATENTEDJuL22w1s ,895, 752 sum 2 FIG. 3

FIG. 2

EXPLOSIVE POWDER DRIVEN SETTING GUN WITH SILENCING DEVICE SUMMARY OF THE INVENTION The present invention is directed to a silencing device for an explosive powder driven setting gun for driving bolts, studs, nails and the like into a target material and, more particularly, it is directed to the ar rangement of passageways located within the barrel of the setting gun for discharging the gases generated when the setting gun is fired.

Silencers of various types have been used on setting guns. However, the various silencers used to date have been unsatisfactory as far as the silencing effect is concerned.

Silencers formed of a pipe section with outflow openings directed to the exterior of the setting gun, that is, to the atmosphere about the setting gun, have, in addition, considerable handling problems.

When a setting gun is being used, the operator holds at least one hand on the pipe section forming the outer jacket of the setting gun. After the setting gun is fired, hot gases generated in the firing operation, which are laden with combustion residues, flow at high pressure through the outflow openings in the outer jacket of the gun and strike the hand of the operator. The hot gases tend to burn the hand of the operator as well as soiling it. The outflow openings not covered by the operators hand, have the effect that the sound waves, which are perceived as an explosion, propagate from the setting gun into the surrounding open space.

Setting guns are frequently used in the heavy construction industry and, naturally, receive rather rough handling. The setting guns are placed, for example, in dirty tool chests or are thrown on dirty surfaces. As a result, the laterally located outflow openings are clogged and particles, for example, sand grains, find their way into the interior of the setting gun and cause considerable operating difficulties.

Therefore, the present invention is directed to the problem of providing a simple silencing means for use on explosive powder driven setting guns utilized on construction sites.

In accordance with the present invention, a silencing device is afforded with gas outlet passages opening into the bore in the barrel and the passages are located closer to the muzzle end of the barrel than the connecting passages which initially remove the explosive gases from the bore. Good results have been obtained with a silencer arrangement in which three connecting passages are arranged equiangularly spaced apart about the surface of the bore. Preferably, the connecting passages are located in the rearward portion of the barrel or piston guide and are located forwardly of the section within the barrel which forms the combustion chamber.

The barrel or the combination of the barrel and a pipe sleeve form an axially extending ring-shaped slot which receives the explosion gases from the connecting passages and in which they contact the inwardly directed surface of the slot for deflecting the gases through gas outlet passages connecting the ring-shaped slot to the bore within the barrel. Within the bore the gases again change direction and flow out of the muzzle end of the barrel. Each change in direction of the gas flow causes a deceleration and expansion of the gases and, thus, contributes considerably to the silencing effectv In such an arrangement there is the additional advantage that the hot gases, instead of issuing laterally from the gun jacket, flow out of the muzzle end of the barrel in the driving direction and, as a result, are completely harmless with respect to the operator handling the gun.

To permit the cleaning of soil residues from the ringshaped slot and the gas outlet passages, the gun jacket is formed by an outer pipe section preferably detachably connected in a known manner about the barrel, for example, by a screw thread. Increased stability for the setting gun is achieved by providing a large diameter muzzle flange at the forward end of the pipe section.

To prevent, as far as is possible, punctiform heating of the enclosing pipe section by the hot explosion gases striking against it, that is, the concentrated heating of a limited area at the point at which the gases would impinge perpendicularly against the pipe section, the connecting passages leading the gases from the bore are directed forwardly at an acute angle to the longitudinal axis of the gun so that the gas is not aimed directly at the surface of the pipe section.

Preferably, the gas outlet passages are located in radial planes staggered angularly with regard to the radial planes containing the connecting passages. The individual explosion gas currents entering the ring-shaped slot from the connecting passages impinge at a high velocity against the inner surface of the pipe section defining the outer surface of the slot and are separated into partial currents. The partial currents bounce off the inner surface of the pipe section and start to whirl about until they flow through the closest gas outlet passage into the bore within the barrel.

Particularly good results are obtained if the same number of gas outflow passages and connecting passages are used and if each gas flow passage is equiangularly spaced from two connecting passages.

As a rule, several different sizes of propellent charges are used for each setting gun for use in different situations. With a weak charge, a lower gas pressure is produced and the velocity of flow is lower than with a more powerful charge. The velocity of the gases flowing through the connecting passages into the ringshaped slot is a determining factor for the distance from the inlet openings of the connecting passages in which eddies are formed.

The gas outflow passages can be arranged and designed differently to correspond to the different outflows based on the strength of the charge used and this factor is of decisive importance in providing the silencing effect. Gas outflow passages in the form of slots extending in the longitudinal direction parallel to the axis of the barrel have proved particularly effective. However, good results have also been obtained with bores arranged in series. The explosion gases flowing into the bore from the gas outflow passages tend to pass to the exterior ofthe gun through its muzzle, that is, in the firing direction, regardless of whether the gun uses a driving piston. In setting guns using a driving piston, the piston shaft seals off the muzzle bore in the driving direction so that the gases tend to accumulate in the bore under certain circumstances and have difficulty in being discharged. To prevent this situation, one or a number of outflow openings are provided which extend from the bore to the outside of the barrel and they are arranged in the forward end of the barrel to facilitate the discharge flow of the gases. It is irrelevant whether the outflow openings are provided in the barrel itself or, for example. in the bore of a pipe section designed as a muzzle flange. It is particularly effective if the number of outflow openings correspond to the number of gas outflow passages from the ring-shaped slot into the bore.

Preferably. the outflow openings are arranged in the same radial planes with the gas outflow passages. In this way a direct deflection of the expanded but still dirtladen gases from the gas outflow passages through the bore to the exterior ofthe gun is achieved. Any further deflection of the gases would have only a minor silencing effect and would result in the deposition of considerable amounts of residue within the interior of the gun.

Basically, the cross sectional form of the outflow openings can be selected at random. Preferably, particularly in piston guns, the outflow openings are designed as grooves formed in the surface of the bore and extending parallel to its axis for increasing the cross sectional area of the bore at the gun muzzle. Such an arrangement is advantageous for maintenance purposes as well as for operating and manufacturing purposes. Accordingly, the cleaning of the outflow openings is very simple, since the muzzle bore and the outflow openings can be cleaned of any residue from the explosion gases in a single cleaning step with a circular brush.

In another embodiment of the invention, a gaspermeable insulating material, acoustically inert to explosive powder gases and temperatures, such as mineral wool, is positioned within the ring-shaped slot. The insulating material affords additional sound absorption and the filtration of solid substances. The filtering effeet is obtained, since the bulk of the combustion residue adheres to the relatively large surfaces of the insulating material. By removing the pipe section laterally enclosing the barrel, it is easy to replace spent insulat ing material with clean material. The filtering effect is of particular advantage if the setting gun is used in an environment where a considerable amount of dirt is likely to find its way into the gun.

For increasing the silencing effect, it is preferable to divide the ring-shaped slot with fins or other dividing elements so that several silencing chambers are formed interconnected with one another. In such an arrangement, the higher pressure ofthe gases entering the ringshaped slot is throttled in the resulting intervals, which can be segment-shaped, and, as a result, leads to considerable silencing of the explosion within the setting gun. Further, a filtering effect is provided in such an arrangement. In this arrangement it is only necessary to remove the outer enclosing pipe section from the barrel for cleaning the silencing chambers. There is no replacement of parts necessary.

The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which there are illustrated and described preferred embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWING In the drawing:

FIG. 1 is a partial longitudinal sectional view of the forward part of an explosive powder driven setting gun, embodying the present invention;

FIG. 2 is a transverse sectional view of the gun shown in FIG. I taken along the line IIII; and

FIG. 3 is a transverse sectional view of the gun shown in FIG. 1 taken along the line III-III;

FIG. 4 is a partial longitudinal sectional view of another embodiment of the setting gun illustrated in FIG.

FIG. 5 is a transverse sectional view, similar to FIG. 2, of another embodiment of the setting gun; and

FIG. 6 is a partial longitudinal sectional view of still another embodiment of the setting gun shown in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION As illustrated in FIG. 1, the setting gun includes a barrel 1 forming an axially elongated bore 2. A driving piston 3 is axially displaceably positioned within the bore, and as shown in FIG. 1, is in its forward position within the bore having driven a fastening element 4 into the receiving material 5. When the gun is ready to be fired, the piston 3 is displaced axially rearwardly through the bore 2, relative to its position in FIG. I, so that its head 9 is located within the rearward section 11 of the bore 2.

At the forward end of the barrel 1, a pipe section 7 is secured to the barrel by means of a thread 8 and has a muzzle flange 6 which extends radially outwardly from the barrel and the pipe section and also extends forwardly of the muzzle end of the barrel into contact with the receiving material 5. Within the barrel, the bore, extending rearwardly from the muzzle end of the barrel, forms a guide for the driving piston 3 which has a diameter substantially the same as that of the forward or leading end of the driving piston. At the rearward end of the guide section of the bore an enlarged diameter section I3 is provided which also has a larger diameter than the rearward section 11.

An axially extending portion of the outer surface of the barrel, extending rearwardly from the muzzle end, is in spaced relationship from the inner surface of the pipe section 7 so that an axially extending ring-shaped slot 17 is provided between the two. The forward end of the section 13 within the bore 2 is connected to the ring-shaped slot by three connecting passages 14, equiangularly spaced apart from one another. Forwardly from the inlet ends of the connecting passages 14 into the ring-shaped slot l7, three gas outlet passages 18 are formed communicating between the ring-shaped slot and the bore within the barrel. The gas outlet passages have a slot like configuration extending in the longitudinal direction of the barrel. At the forward ends of the gas outlet passages, note FIGS. 1 and 3, outlet openings 19 are provided which extend in the longitudinal direction of the barrel parallel to its axis and terminate at the muzzle end of the barrel.

In driving an anchoring element into the receiving material 5, a propellent or explosive powder charge, not shown, is ignited at the rearward end of the bore, that is, the end opposite the muzzle end of the barrel. At the time the gun is fired, the driving piston has its head 9 located in the section 11 of the bore and this section has the same diameter as the head. Accordingly, the trailing end face 12 of the piston head 9 forms a wall of closed combustion chamber within the barrel.

The explosion gases generated when the gun is fired, exert a pressure on all of the surfaces within the closed combustion chamber and drive the axially displaceable piston 3 and the fastening element 4 in the direction of the receiving material 5. As the piston 3 accelerates within the barrel, its head 9 enters the larger diameter section 13 of the bore 2 and the explosion gases are then free to flow forwardly between the lateral surfaces of the head 9 and the surface of the bore 2 under a relatively high pressure into the connecting passages 14. As can be seen in FIG. 1, the connecting passages extend generally in the direction of the axis of the barrel, however, they diverge outwardly at an acute angle to the longitudinal axis of the barrel into the ring-shaped slot 17 defined by the inner surface 15 of the pipe section and the recessed outer surface 16 of the barrel. Due to the orientation of the connecting passages 14, the explosion gases flow generally in the axial direction of the bore and are directed at an acute angle against the inner surface 15 of the pipe section 7.

As the explosion gases flow through each of the connecting passages 14 and impinge against the inner surface lS of the pipe section they are divided into separate flow currents. These flow currents of the gases begin to whirl within the ring slot 17 and then flow through the gas outlet passages 18. As can be seen in FIG. 2, the gas outlet passages are located in radial planes displaced angularly from the radial planes of the connecting passages. Within the gas outlet passages 18 the explosion gases flow along the periphery of the bore 2. From the gas outlet passages 18 bordering the bore 2, the explosion gases, already considerably expanded, exit from the barrel in the driving direction of the gun, after another change in direction, and flow outwardly through the outlet openings 19 over the exterior surface of the piston shaft 21.

As can be seen in FIG. 3, the outlet openings 19 are formed as grooves in the inner surface at the forward or muzzle end of the bore and are arranged in radial planes aligned with the radial planes containing the gas outlet passages.

In the embodiment shown in the drawing, a driving piston is used in inserting the anchoring element 4 into the receiving material, however, it is also possible to drive the fastening or anchoring element without the use of a piston and the anchoring element itself affords the corresponding function of the driving piston. As far as the sound-absorbing effects are concerned, the results obtained in a setting gun without a driving piston are the same as those in which a driving piston is used.

While specific embodiments of the invention have been shown and described in detail to illustrate the application of the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles.

in FIG. 4 mineral wool 30, a gas-permeable insulating material, is positioned within the ring-shaped slot 17. The insulating material affords additional sound absorption along with filtration of solid substances.

In FIG. 5 fins 32 extending radially outwardly from the barrel 1 within the ring shaped slot 17 have their outer edges spaced inwardly from the inner surface of the pipe section 7 and, in combination with the axially extending partitions 34, divide the slot into a plurality of interconnected silencing chambers.

We claim:

1. An explosive power driven setting gun for driving anchoring members, such as bolts, studs, nails and the like, into a target material, comprising an axially elongated barrel forming a bore and having a forward muzzle end and an oppositely disposed rearward end, a sleeve extending in the axial direction of said barrel and secured to and laterally enclosing said barrel for a portion of its axial length forwardly of the rearward end of its bore, an axially extending portion of the outer surface of said barrel disposed in spaced relationship to the inner surface of said sleeve and forming therebetween an axially extending ring-shaped slot about said barrel radially outwardly from said bore, at least one connecting passage extending through said barrel between the bore therein and said ring-shaped slot, at least one gas outlet passage located in said barrel radially inwardly of said ring-shaped slot and communicating between said ring-shaped slot and the bore in said barrel, said gas outlet passage located closer to the forward end of said bore than said connecting passage, said bore having a larger diameter adjacent the rearward end of said barrel than the portion of said bore which extends rearwardly from said forward end toward said rearward end, said ring-shaped slot located laterally about the smaller diameter end of said bore extending rearwardly from the forward end of said barrel, and said connecting passage extending from the larger diameter portion of said bore to said ring-shaped slot.

2. An explosive powder driven setting gun for driving anchoring members, such as bolts, studs, nails and the like, into a target material, comprising an axially elongated barrel forming a bore and having a forward muzzle end and an oppositely directed rearward end, a sleeve extending in the axial direction of said barrel and secured to and laterally enclosing said barrel for a portion of its axial length forwardly of the rearward end of said bore, an axially extending portion of the outer surface of said barrel disposed in spaced relationship to the inner surface of said sleeve and forming therebetween an axially extending ring-shaped slot about said barrel radially outwardly from said bore, a plurality of connecting passages extending through said barrel between the bore therein and said ring-shaped slot, a plurality of gas outlet passages located in said barrel radially inwardly of said ring-shaped slot and communicating between said ring-shaped slot and the bore in said barrel, said gas outlet passages spaced from said connecting passages toward the forward end of said bore, the plurality of said gas outlet passages are spaced angularly apart, said connecting passages are located in radial planes extending through the axis of said barrel, said gas outlet passages are located in radial planes extending through the axis of said barrel and the radial planes containing said connecting passages are spaced angularly apart from the radial planes containing said gas outlet passages, and at least one outlet opening formed in said barrel and opening from said bore into the forward end of said barrel so that gas within the bore can flow outwardly therefrom through said outlet opening and out of the forward end of said barrel.

3. An explosive powder driven setting gun, as set forth in claim 2, wherein a plurality of said outlet openings are provided in said barrel corresponding to the number of said gas outlet passages and each said outlet opening is aligned with a different one of said gas outlet passages.

4. An explosive powder driven setting gun, as set forth in claim 3, wherein said outlet openings are formed as axially extending grooves in the surface of the bore in said barrel and extend from the ends of said gas outlet passages closer to the forward end of said barrel to the forward end of said barrel,

5. An explosive powder driven setting gun for driving anchoring members, such as bolts. studs, nails and the like, into a target material, comprising an axially elongated barrel forming a bore and having a forward muzzle end and an oppositely directed rearward end, a sleeve extending in the axial direction of said barrel and secured to and laterally enclosing said barrel for a portion of its axial length forwardly of the rearward end of its bore, an axially extending portion of the outer surface of said barrel disposed in spaced relationship to the inner surface of said sleeve and forming therebe tween an axially extending ring-shaped slot about said barrel radially outwardly from said bore, a plurality of connecting passages extending through said barrel between the bore therein and said ring-shaped slot, a plurality of gas outlet passages located in said barrel radially inwardly of said ring-shaped slot and communicating between said ring-shaped slot and the bore in said barrel, said gas outlet passages spaced from said connecting passages toward the forward end of said bore, the plurality of said gas outlet passages are spaced angularly apart, said connecting passages are located in radial planes extending through the axis of said barrel, said gas outlet passages are located in radial planes extending through the axis of said barrel and the radial planes containing said connecting passages are spaced angularly apart from the radial planes containing said gas outlet passages, and a gas-permeable insulating material acoustically inert to the gases and temperatures generated in an explosive powder driven setting gun is 8 located within said ring-shaped slot.

6. An explosive powder driven setting gun for driving anchoring members, such as bolts, studs, nails and the like, into a target material, comprising an axially elongated barrel forming a bore and having a forward muzzle end and an oppositely directed rearward end, a sleeve extending in the axial direction of said barrel and secured to and laterally enclosing said barrel for a portion of its axial length forwardly of the rearward end of its bore, an axially extending portion of the outer surface of said barrel disposed in spaced relationship to the inner surface of said sleeve and forming therebetween an axially extending ring-shaped slot about said barrel radially outwardly from said bore, a plurality of connecting passages extending through said barrel between the bore therein and said ring-shaped slot, a plurality of gas outlet passages located in said barrel radially inwardly of said ringshaped slot and communicating between said ring-shaped slot and the bore in said barrel, said gas outlet passages spaced from said con necting passages toward the forward end of said bore, the plurality of said gas outlet passages are spaced angularly apart, said connecting passages are located in radial planes extending through the axis of said barrel, said gas outlet passages are located in radial planes extending through the axis of said barrel and the radial planes containing said connecting passages are spaced angularly apart from the radial planes containing said gas outlet passages, and means are arranged within said ring-shaped slot for dividing said ring-shaped slot into a plurality of individual interconnected compartments.

7. An explosive powder driven setting gun, as set forth in claim 6, wherein said means for dividing said ring-shaped slot are fins.

Claims

1. An explosive power driven setting gun for driving anchoring members, such as bolts, studs, nails and the like, into a target material, comprising an axially elongated barrel forming a bore and having a forward muzzle end and an oppositely disposed rearward end, a sleeve extending in the axial direction of said barrel and secured to and laterally enclosing said barrel for a portion of its axial length forwardly of the rearward end of its bore, an axially extending portion of the outer surface of said barrel disposed in spaced relationship to the inner surface of said sleeve and forming therebetween an axially extending ringshaped slot about said barrel radially outwardly from said bore, at least one connecting passage extending through said barrel between the bore therein and said ring-shaped slot, at least one gas outlet passage located in said barrel radially inwardly of said ring-shaped slot and communicating between said ring-shaped slot and the bore in said barrel, said gas outlet passage located closer to the forward end of said bore than said connecting passage, Said bore having a larger diameter adjacent the rearward end of said barrel than the portion of said bore which extends rearwardly from said forward end toward said rearward end, said ring-shaped slot located laterally about the smaller diameter end of said bore extending rearwardly from the forward end of said barrel, and said connecting passage extending from the larger diameter portion of said bore to said ring-shaped slot.

4. An explosive powder driven setting gun, as set forth in claim 3, wherein said outlet openings are formed as axially extending grooves in the surface of the bore in said barrel and extend from the ends of said gas outlet passages closer to the forward end of said barrel to the forward end of said barrel.

5. An explosive powder driven setting gun for driving anchoring members, such as bolts, studs, nails and the like, into a target material, comprising an axially elongated barrel forming a bore and having a forward muzzle end and an oppositely directed rearward end, a sleeve extending in the axial direction of said barrel and secured to and laterally enclosing said barrel for a portion of its axial length forwardly of the rearward end of its bore, an axially extending portion of the outer surface of said barrel disposed in spaced relationship to the inner surface of said sleeve and forming therebetween an axially extending ring-shaped slot about said barrel radially outwardly from said bore, a plurality of connecting passages extending through said barrel between the bore therein and said ring-shaped slot, a plurality of gas outlet passages located in said barrel radially inwardly of said ring-shaped slot and communicating between said ring-shaped slot and the bore in said barrel, said gas outlet passages spaced from said connecting passages toward the forward end of said bore, the plurality of said gas outlet passages are spaced angularly apart, said connecting passages are located in radial planes extending through the axis of said barrel, saiD gas outlet passages are located in radial planes extending through the axis of said barrel and the radial planes containing said connecting passages are spaced angularly apart from the radial planes containing said gas outlet passages, and a gas-permeable insulating material acoustically inert to the gases and temperatures generated in an explosive powder driven setting gun is located within said ring-shaped slot.

6. An explosive powder driven setting gun for driving anchoring members, such as bolts, studs, nails and the like, into a target material, comprising an axially elongated barrel forming a bore and having a forward muzzle end and an oppositely directed rearward end, a sleeve extending in the axial direction of said barrel and secured to and laterally enclosing said barrel for a portion of its axial length forwardly of the rearward end of its bore, an axially extending portion of the outer surface of said barrel disposed in spaced relationship to the inner surface of said sleeve and forming therebetween an axially extending ring-shaped slot about said barrel radially outwardly from said bore, a plurality of connecting passages extending through said barrel between the bore therein and said ring-shaped slot, a plurality of gas outlet passages located in said barrel radially inwardly of said ring-shaped slot and communicating between said ring-shaped slot and the bore in said barrel, said gas outlet passages spaced from said connecting passages toward the forward end of said bore, the plurality of said gas outlet passages are spaced angularly apart, said connecting passages are located in radial planes extending through the axis of said barrel, said gas outlet passages are located in radial planes extending through the axis of said barrel and the radial planes containing said connecting passages are spaced angularly apart from the radial planes containing said gas outlet passages, and means are arranged within said ring-shaped slot for dividing said ring-shaped slot into a plurality of individual interconnected compartments.