US3566978A

US3566978A - Apparatus for driving anchoring elements for a predetermined depth of penetration

Info

Publication number: US3566978A
Application number: US792033*A
Authority: US
Inventors: Karl-Ernst Udert
Original assignee: Hilti AG
Current assignee: Hilti AG
Priority date: 1968-01-29
Filing date: 1969-01-17
Publication date: 1971-03-02
Anticipated expiration: 1988-03-02
Also published as: FR1595405A; DE1603852C3; DE1603852B2; GB1242458A; DE1603852A1

Abstract

An arrangement for driving anchoring elements into a target material to obtain a predetermined reproducible depth of penetration is achieved by providing a driving force in excess to that necessary to fix the anchoring elements in place. After an anchoring element is driven to a predetermined depth the excess energy supplied is transformed into thermal energy by placing the member driving the anchoring element in frictional contact with a stop member. The portion of the excess energy not transformed into thermal energy is transferred from the stop member to another member.

Description

United States Patent Karl-Ernst Udert Triesen, Liechtenstein Jan. 17, 1969 Mar. 2, 1971 Hilti Aktiengesellschaft Schaan Furstentum, Liechtenstein Jan. 29, 1968 Germany Inventor Appl. No. Filed Patented Assignee Priority APPARATUS FOR DRIVING ANCHORING ELEMENTS FOR A PREDETERMINED DEPTH OF PENETRATION 8 Claims, 3 Drawing Figs.

U.S. Cl 173/139,

227/10 Int. Cl B25c 1/14 Field of Search 173/ 1 I5,

References Cited UNITED STATES PATENTS l/l943 Amtsberg et al 173/139 2,836,247 5/1958 McCulloch 166/237X 2,845,908 8/1958 Maier 60/26.] 3,016,539 1/1962 Marsh et a1. 227/10 3,115,637 12/1963 Elliott 227/10 3,297,224 1/1967 Osborne... 227/10 3,465,942 9/1969 Diehl 227/10 3,469,504 9/1969 Neighorn 173/139X FOREIGN PATENTS 858,618 5/1958 Great Britain 173/139 Primary Examiner- Ernest R. Purser Attorney-McGlew and Toren PATENIED m 2 SHEET 2 [1F 3 APPARATUS FORDRIVING ANCHORING ELEMENTS FORA PREDETERMINED DEPTH OF PENETRATION SUMMARY OF THE INVENTION With guns employing axially displaceable hammer pistons for insertinganchoring elements into a hard target material, such astthe type mentionedfabove, a certain reproducible depth of penetration cannot be achieved when inserting anchoring elements. such as bolts'and the like. This results from several factors, for instance, the strength of the target materialis not uniform, for example, in steel characterized as St37 the strength can range between 37 -45 kp/qmm, and further, the thicknesses of the cartridges employedalso effects the depth of penetration achieved. Accordingly, based on the. strength of the target material at thepoint of insertion of the anchoring element and also the thicknesstof.thecartridge used in driving the anchoringelement, the depth of penetration into the target material will vary. In certain methods of fastening anchoring elements this inability. to provide a, reproducible: depth of penetration is disadvantageous. If: it is attemptedto. obtain a uniform depth of penetration with known guns of the; type mentioned above, for example, by varying the initial. combustion space, then, initially, it would be necessary to; determine the strength of the target material at the point of insertion of the anchoring element. Such. an arrangement for:

setting anchoring elements would be. time consuming and cumbersome. Another possible solution of this'problemwould. be to use the undamped impact, that is, by stopping the hammer piston at a certain. point andtransmitting the entire kinetic energy of the piston to another axially moving part. However, this arrangement cannot be realizedwith any justifiable expenditure in a device for setting anchoring elements because of the greater forces whichare developed in such a device.

Therefore, the primary object of the present invention is to provide an arrangement for achievinga reproducible depth of penetration of anchoring elements into a target material.

Another object of the invention is to usean excess amount of kinetic energy in driving the anchoringelement intothe tar.- get material and, after the insertion of the anchoring element-,. transforming at least a major portion of the excess kinetic energy into thermal energy.

Still another object of the invention is to provide a spring arrangement for. absorbing a portion of. the excess energy employed in driving the anchoring elements.

Yet another object of the invention is to supply the driving. piston and a stop member with frustoconically shaped surfaces for frictional interengagement when the hammer piston has driven the anchoring element into the target material for a. predetermined depth.

Accordingly, in the present invention kinetic energy is transmitted to a hammer piston ina quantity in excess of that required to provide a predetermined reproducible-depth of penetration of the anchoring elements. After the hammer piston has inserted the anchoring elementfor the predetermined depth the excess kinetic energy is transformed into thermal energy when the hammer piston passes into frictional. contact with a suitably shaped stop member. The stop member is elastically deformable and the thermal energy is developed due to the frictional contact between the hammer piston and the stop member as the stop member'travels througha short path because of its elastic deformation. Any residual kinetic. energy transferred from the hammer piston to the stop. member and nottransferred into thermal energy is transmitted to means operatively positionedbetween the stop memberandf the housing.

Since the amount of kinetic energy transmitted to the hammer piston is greater than that necessary to achieve the depth of penetration, the required depth of penetration of the anchoring element is obtainable in every instance. Accordingly, once the anchoring element has been driven to the predetermined depth by the hammer piston the excess kinetic energy can be removed from the hammer piston. In the present invention it has been recognized that it is advantageous to transform a major portion of the excess kinetic energy, for example, about two-thirds, into thermal energy. The change of the kinetic energy supplied to the hammer piston into thermal energy is accomplished by affording frictional contact between the hammer piston and'a stop member against whichthe hammer piston impacts when it has attained the desired depth of penetration for the anchoring elements. The hammer piston is arranged to extend through the stop member in achieving theiinsertion of the anchoringelement.

Preferably, the stopmember is formed of springsteel which is elastically deformable,when=the hammer piston strikes the stop member, and as aresult, a reproducible path is available for the hammer piston. Due to the reproducible path, the forces to be absorbedby the stopmember and the hammer piston do notbecome too great. Moreover, this fact is ofconsiderable importance, since because of the possibly light weight of the device the stop member and the hammer piston can becorrespondingly dimensionedwithin justifiable limits in accordance withtheforces to be absorbed. However, the interception path affordedby the stop member should not be too short since this path provides the tolerance required. for: the depth of penetration.

The residual portion of the excess kinetic energy, which. is. nottransformed into thermalgenergy, is transmitted to a body in operative connection with the housing partwhose mass is of such anextent that the inertia of the body is sufficient to absorb the residual kinetic energy.

In constructing the apparatus, in accordance with the present invention, both the hammer pistonv and the stop member are each provided with a frustoconically shaped surface converging in the firing direction of thedevice with the surfaces arranged-to be in frictional contact after the desired depth of penetration of the anchoring element has been.

achieved. Further, the elastically defonnable stop memberis supported within the device by the member which is arranged to absorb the excess kineticenergy not transformed into thermal energy.

Due to the frustoconical arrangement of thecontacting surfaces of the stop member and the hammer piston a force is exertedin the radial direction when the hammer piston impacts against the stopmember which causes the stop member to widen. By providingacertain amount of radial play for the stop member within the member supporting it, and by properly dimensioning. the stop member, it is only elastically deformed when it is struck by the hammer piston. Because of the bearing arrangement of the stop member on the member within the housing and the. interengagement of the member withthe housing, the excess kinetic energy which is not trans-- formed into thermal energy is readily transmitted to the member.

For improved absorption of the forces transmitted from the hammer piston to the stop member and also to improve the dimensioning of the stop member and the hammer piston, the stop member is provided with a second frustoconically arranged surfacediverging in the firing direction and mounted on a frustoconically shaped inner ring to provide both elastic. deformation and'axialdisplacement. In this arrangement the inner ringbears directly against the member within the housing which absorbs the excess kinetic energy from the stop member.

If the excess energy transmitted by the hammer piston. is.

greater than about 8 kprn, several elastically deformable inner and outer rings are disposed in an alternatingarrangement extending between the member supporting the stop; member and another member in engagement with thehousing of the device. Inthis arrangement the outer faces of theinner materials.

Another feature of the apparatus, in accordance with the present invention, concerns the possible damage to impactsensitive materials, such as wood, plastics, and the like, and

also to thin metal plates, which can be avoided by mounting the parts of the apparatus within the housing so that they are axially displaceable and, as a result, do not exert a direct impact on the housing and in turn on the target material when the excess kinetic energy is transferred from the hammer piston. To afford this axial displacement without affecting the housing of the apparatus, a pair of spring members are disposed within the housing for absorbing or resiliently mounting the various parts of the apparatus within the housing. These annular springs and, in addition, the inner and outer rings afford a transformation of the excess energy into thermal energy. In the apparatus, a guide member is provided at the firing end which is axially displaceable within the housing under the impact provided by the hammer piston to avoid damage to the target material.

In devices or guns for inserting the anchoring elements which are provided with pressure safety devices, the guide member is connected to the housing preferably by means of a catch. The force of the catch is so great that the contact pressure is overcome, without the guide part being displaced relative to the housing part.

In inserting the anchoring elements to a predetermined length the hammer piston can be adjusted preferably by varying it to a minor extent by shifting the housing part containing the piston and stop member.

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 specification. 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 DRAWINGS In the drawings:

FIG. 1 is a longitudinal sectional view of the front or firing end of a device for inserting anchoring elements illustrating one embodiment of the invention;

FIG. 2 is a longitudinal sectional view similar to that shown in FIG. 1 illustrating a second embodiment of the present invention; and

FIG. 3 is a longitudinal sectional view of an alternate arrangement for securing the forward end of the device, shown in FIGS. 1 and 2, in position.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, a device 3 for inserting anchoring elements into a target material is formed of a housing member 1 secured to the device 3 by means of threads 2. Located in the forward or firing end of the housing member 1 is a guide member 4 for aligning the anchoring elements prior to the insertion operation. Within the housing member I, at its rearward end, a member 5 is secured to the housing member by shear pins 6. The member 5 extends transversely across the housing member 1. In its rearward face a recess 5a is formed in the member 5 and an opening 5b extends forwardly from the recess through the member. Located within the recess 5a is a stop member 7 with a certain amount of radial play provided between the outer periphery of the stop member and the juxtaposed surface of the recess. A hole or opening 7' is formed through the stop member 7 coaxial with the opening 511 through the member 5. The rearward portion of the opening 7 has a frustoconically shaped surface 7 a which is in converging relationship in the firing direction of the device. Mounted for axial displacement through the device 3 and the housing member I is a hammer piston 8 which, as shown in FIG. I, has its forward end supported within the guide member 4. Near its rearward end the hammer piston 8 has a frustoconically shaped surface portion 8a which is arranged to engage the correspondingly tapered surface 7a of the stop member 7. As can be noted, the surface 7a within the stop member and the surface 8a on the hammer piston are arranged in contacting engagement when the hammer piston is driven forwardly through the device 3 by an explosive force for driving an anchoring element, not shown, from the guide member 4 of the device.

In the device illustrated in FIG. I, when the hammer piston 8 has driven the anchoring element into the target material for the predetermined depth of penetration the frustoconically shaped surface 8a on the hammer piston impacts against the similarly shaped frustoconically surface of the stop member. As a result, the kinetic energy in excess of that required for the insertion of the anchoring element is transferred over a path determined by the elastic deformation of the stop member 7 within the recess 5a of the member 5. Due to the frictional contact between the

corresponding surfaces

7a and 8a the major portion of the kinetic energy is transformed into thermal energy. However, that portion of the kinetic energy which is not transformed into thermal energy is transferred through the stop member 7 to the member 5 which is secured to the housing member 1 by means of the shear pins 6 and thus to the remainder of the device. The shear pins 6 are dimensioned to shear when considerable excess energy is developed in the member 5 and before any of the other parts in the device are overstressed and damaged.

In FIG. 2 a second embodiment of the invention is set forth which operates in generally the same manner as the embodiment in FIG. 1, however, the arrangement is somewhat more elaborate and provides for a greater absorption of excess energy by spring means within the housing member.-This second embodiment is formed of a housing member 101 engaged by means of threads 102 on the front end of a device 103. At the forward or firing end of the housing member a guide member 104 is resiliently positioned. I

Within the rearward interior end of the housing member 101 a member 105 is positioned. As with the member 5 in FIG. 1 the member 105 has an axially arranged recess 105a extending forwardly from its rearward end and being axially located relative to the housing member 101. Positioned within the recess 105a is a stop member 107 having an axial opening 107' extending therethrough and aligned with a similar opening 105k in the forward end of the member 105. The opening through the stop member 107 has a first frustoconically shaped surface 107a and a second serially arranged frustoconically shaped surface l07b. The surface 107a extends from the rearward end of the stop member for a portion of its length and the remainder of the opening through the stop member is provided by the second surface l07b. While the surface 107a converges in the firing direction the second surface 107k diverges in the firing direction and provides an open space within which a frustoconically shaped ring member is positioned having its opening in axial alignment with the the frictional through the device 107 and the housing member 101. Within the housing member the hammer piston passes axially through thespring 107 in the stop member, the opening in the ring member 11512, the opening 105 in-the member 105 and the guidemember 104. Near its rear end the hammer piston 108 .has a frustoconically shaped surface 108a, converging in the firing direction, which impacts against the surface 107a of the stop member 107. e

At its forward end the member 105 has a smaller outside diameter than its rear 'portion providing an annular space between its outer surface and the opposite inner surface of the housing member 101. Within this annular space and extending from the member 105 toward the forward end of the housing member 101 are a plurality of inner rings 110 and outerrings 111 disposed in an alternating arrangement. The outer face s of theinner rings and the inner faces of the outer rings taper in both directions from a midpoint. As can be noted in-FIG. 2, the tapered faces of the alternating inner and outer rings each contacts a similarly tapered surfaceon the adjacentrings, for example each full inner ring contacts two outer rings, one

above it and one below it, as seen in FIG. 2, and the same is true for each full outer ring. In this. arrangementthe tapered faces tend to ride on one another when the inner and .outer rings are disposed in a compressed relationship. 1

At the rearward end of the alternating inner and outer rings, a half inner ring 110a bears against the'member 105 while at the opposite end of the rings a half outer ring 111a .bears against asleevelike member 113 whichhas a diameter. slightly less than that of the inner rings so that it is positioned inwardly of the rings. At its forward end the sleevelike member 113 has a radially outwardly directed flange 113a which extends into contact with the inner surface of the housing member 101. At its rearward end the sleevelike member 113-has a radially inwardly :directed flange 113b which extends inwardly toward but is spaced from the outersurface of the guide member 104 at its rearward end. A first helical spring 114 bears against the inner forward face of the housing member 101 and extends rearwardly within the sleeve 113 and bears against the flange 11312. Spaced inwardly from the first spring 114 is a second helical spring 116 which bears against a shoulderformed on the guide member 104 and extends rearwardly and bears against the member 105 within a recess 105c'formed in its for ward face. 1

As mentioned previously, the housing member 101 is in threaded engagement with the remainder of the device 103. to afford a fine adjustment for the hammer piston stroke. When the hammer piston stroke is suitably adjusted a screw 120 can be engaged within a slot 103a in the threaded end of the device 103 to assure that the housing member 101 is secured against any accidental turning and displacement.

In operation the hammer piston 1.03 rides forwardly guided within the bore through the device 103, the ring 115, and the guide member 104 for inserting an anchoring member into a target material. Since the explosive force which drivesthe hammer piston forwardly through the device supplies an amount of kinetic energy in excess of that required for driving the anchoring element for its predetermined depth of penetration, when the predetermined depth of penetration has been achieved, the frustoconically shaped surface 108a on the hammer piston impacts against the similarly shapedsurface 107a of the stop member and elastically deforms the stop member. While the action of the hammer piston 108 in the driving or firing direction against the stop member 107 tends to move the stop member in the firing direction and to causeit to widen at the same time the surface 107b of the stop member provides a compressing action on the inner ring 115. Due to contact between the surfaces 1 07a onthe stop member and the surface 108a on the hammer piston and similarly between the surface 115 a on the ring 115 and the surface 107k of the stop member, a major portion of the ,excess kinetic energy of the hammerpiston is transformed into thermal energy. By employing the frustoconically shaped ring 115 the stop member 107 and the hammer piston 108 can be more easily dimensioned because the forces becomes smaller due to the longer interception path provided by this arrangement.

The remaining kinetic energy transferred to the stop member from the hammer piston'is conveyed through the ring member 115 to the member which is in sliding contact with the walls of the housing member 101. The force or energy exerted on the member 105 tends to press forwardly against the spring 116 which bears at its forward end against the guide member 104. In addition, the member 105 also exerts a force in the forward direction against the combined inner and

outer rings

110, 111 which at their forward end bear against the flange 113a of the sleeve member 113. The inner and outer rings ride forwardly with the sleeve 113 for distance a compressingthe helical spring 114 until the flange 113a contacts the forward end of the housing member 101 and then the the housing member 201 and the guide 204 which can be employed in guns or devices with a pressure safety device. In this arrangement a number of bores 221 extend through the forward end face of the housing member201 and open at their inner ends into a groove or recess 204a, formed in the exterior surface of the guide member 204. For providinga locking arrangement between the housing member and the guide member, a ball222 is inserted into each bore 221 and a spring member 223 held in place by a retaining pin 224 resiliently urges the ball into locking engagement with the recess 204a and'etains the guide part within the forward end of the housing member.

I claim: 1

1. Apparatus for driving anchoring elements such as bolts, studs, and nails into a hard target material such'as iron, concrete and the like to obtain a predetermined reproducible depth of penetration of the anchoring elements, comprises a housing member, a hammer piston axially displaceably mounted within said housing memherfor driving anchoring elements into the target material in response to an explosive force acting on said hammer piston, means mounted within said housing arrl arranged for receiving energy from said hammer piston, a stop member mounted within said housing and in contact with said means within said housing member, said stop member is elastically deformable and is arranged to be in frictional contact with said hammer piston when said hammer piston has a effected the predetermined depth of penetration of the anchoring elements and said stop member also being in bearing contact with said means when it is in frictional contact with said hammer piston, resilient means being positioned within said housing member for mounting said means inaxially displaceable relationship within said housing member, said resilient means comprisesa plurality of inner rings and a plurality of outer rings disposed within said housing member and being concentrically arranged about the axis of said hammer piston, said inner anclouter rings being arranged in alternating arrangement with the outer faces of said inner rings being in frictional contact with the inner faces of said outer rings, whereby upon achieving the desired depth of penetration of the anchoring element said hammer piston contacts said stop member and the energy from the explosive force in excess of that required for inserting the anchoring element is transformed at least in part into thermal energy by the frictional contact between said stop member and said hammer piston and the portion of the energy not converted into thermal energy is transmitted from said] stop member to said means within said housing member.

2. Apparatus, as set forth in claim 1, wherein the outer faces of said inner rings and the inner faces of said outer rings are tapered relative to the axial direction of said hammer piston and the tapered faces of each of at least a number of said inner rings and said outer rings being in frictional contact with the similarly tapered surface of the adjacent ones of outer and inner rings respectively.

3. Apparatus, as set forth in claim 2, wherein said resilient means comprises a sleeve located within said housing member and spaced inwardly from the inner surface of said inner rings, a radially outwardly extending flange secured to the forward end of said sleeve in the firing direction of the apparatus and extending outwardly into sliding contact with the inner surface of said housing member, at the rearward end of the alternating said inner and outer rings the rearward one thereof contacting said member and at the forward end of said inner and outer rings the forward one thereof contacting said flange on said sleeve.

4. Apparatus, as set forth in claim 3, wherein an axially displaceable guide member being located in the forward end of said housing member in the firing direction of said apparatus.

5. Apparatus, as set forth in claim 4, wherein said resilient means comprises a first helical spring extending between said sleeve and the inner surface of said housing member at its forward end, and a second helical spring extending between said member at the forward end thereof and said guide member.

6. Apparatus for driving anchoring elements such as bolts, studs, and nails into a hard target material such as iron, concrete and the like to obtain a predetermined reproducible depth of penetration of the anchoring elements, comprises a housing member, a hammer piston axially displaceably mounted within said housing member for driving anchoring elements into the target material in response to an explosive force acting on said hammer piston, means mounted within said housing and being arranged for receiving energy from said hammer piston, a stop member mounted within said housing and in contact with said means within said housing member, said stop member is elastically deformable and is arranged to be in frictional contact with said hammer for when said hammer piston has effected the predetermined depth of penetration of the anchoring elements and said stop member also being in bearing contact with said means when it is in frictional contact with said hammer piston, said stop member comprises a first annular part anda second annular part, said second annular part being disposed within said first annular part and located at the end thereof extending in the firing direction of the apparatus, said first and second annular parts having axial arranged-openings therethrough for receiving said hammer piston, whereby upon achieving the desired depth of penetration of the anchoring element said hammer piston contacts said stop member: and the energy from the explosive force is excess of that required for inserting the anchoring element is transformed at least in part into thermal energy by the frictional contact between said stop member and said hammer piston and the portion of the energy not converted into thermal energy is transmitted from said stop member to said means within said housing member.

7. Apparatus, as set forth in claim 6, wherein the interior surface within the opening through said first annular part having a first frustoconically shaped surface extending from the rearward end of said first annular part in the firing direction of the apparatus toward the forward end of said housing member, a second frustoconically shaped surface extending from said first surface in the firing direction of said apparatus, said first frustoconically shaped surface converging in the firing direction and said second frustoconically shaped surface diverging in the firing direction, s and said second annular part having a frustoconically shaped outer surface arranged to engage said second frustoconically shaped surface of said first annular part, the forward end of said second annular part in the firing direction being in contact with same member.

8. Apparatus, as set forth in claim 7, wherein said means cornlprisin a member mounted in said housing member to be axia disp aceable therein, said member having an axially arranged recess in the end thereof directed away from the firing direction of the apparatus, said stop member being spaced within and radially inwardly from the recess in said member for permitting widening of said stop member within said recess.

Claims

1. Apparatus for driving anchoring elements such as bolts, studs, and nails into a hard target material such as iron, concrete and the like to obtain a predetermined reproducible depth of penetration of the anchoring elements, comprises a housing member, a hammer piston axially displaceably mounted within said housing member for driving anchoring elements into the target material in response to an explosive force acting on said hammer piston, means mounted within said housing and arranged for receiving energy from said hammer piston, a stop member mounted within said housing and in contact with said means within said housing member, said stop member is elastically deformable and is arranged to be in frictional contact with said hammer piston when said hammer piston has a effected the predetermined depth of penetration of the anchoring elements and said stop member also being in bearing contact with said means when it is in frictional contact with said hammer piston, resilient means being positioned within said housing member for mounting said means in axially displaceable relationship within said housing member, said resilient means comprises a plurality of inner rings and a plurality of outer rings disposed within said housing member and being concentrically arranged about the axis of said hammer piston, said inner and outer rings being arranged in alternating arrangement with the outer faces of said inner rings being in frictional contact with the inner faces of said outer rings, whereby upon achieving the desired depth of penetration of the anchoring element said hammer piston contacts said stop member and the energy from the explosive force in excess of that required for inserting the anchoring element is transformed at least in part into thermal energy by the frictional contact between said stop member and said hammer piston and the portion of the energy not converted into thermal energy is transmitted from said stop member to said means within said housing member.

6. Apparatus for driving anchoring elements such as bolts, studs, and nails into a hard target material such as iron, concrete and the liKe to obtain a predetermined reproducible depth of penetration of the anchoring elements, comprises a housing member, a hammer piston axially displaceably mounted within said housing member for driving anchoring elements into the target material in response to an explosive force acting on said hammer piston, means mounted within said housing and being arranged for receiving energy from said hammer piston, a stop member mounted within said housing and in contact with said means within said housing member, said stop member is elastically deformable and is arranged to be in frictional contact with said hammer for when said hammer piston has effected the predetermined depth of penetration of the anchoring elements and said stop member also being in bearing contact with said means when it is in frictional contact with said hammer piston, said stop member comprises a first annular part and a second annular part, said second annular part being disposed within said first annular part and located at the end thereof extending in the firing direction of the apparatus, said first and second annular parts having axial arranged-openings therethrough for receiving said hammer piston, whereby upon achieving the desired depth of penetration of the anchoring element said hammer piston contacts said stop member and the energy from the explosive force is excess of that required for inserting the anchoring element is transformed at least in part into thermal energy by the frictional contact between said stop member and said hammer piston and the portion of the energy not converted into thermal energy is transmitted from said stop member to said means within said housing member.

8. Apparatus, as set forth in claim 7, wherein said means comprising a member mounted in said housing member to be axial displaceable therein, said member having an axially arranged recess in the end thereof directed away from the firing direction of the apparatus, said stop member being spaced within and radially inwardly from the recess in said member for permitting widening of said stop member within said recess.