US2554714A

US2554714A - Machine gun testing device

Info

Publication number: US2554714A
Application number: US611497A
Authority: US
Inventors: Glen E Mcpherren
Original assignee: Consolidated Vultee Aircraft Corp
Current assignee: Consolidated Vultee Aircraft Corp
Priority date: 1945-08-20
Filing date: 1945-08-20
Publication date: 1951-05-29
Anticipated expiration: 1968-05-29

Description

May 29;, 1951 G. E. MOPHERREN 2,554,714

MACHINE GUN TESTING DEVICE Filed Aug. 20, 1945 4 Sheets-Sheet 1 May 29, 1951 G. E. MCPHERREN MACHINE GUN TESTING DEVICE Filed Aug. 20, 1945 4 Sheets-Sheet 2 NMMW,

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iii-ii!!! May 29, 1951 G. E. M PHERREN MACHINE GUN TESTING DEVICE 4 Sheets-Sheet 4 Filed Aug. 20, 1945 MNN Patented May 29, 1951 UNITED STATES MACHINE GUN TESTING DEVICE,

Glen E. McPherren, San Diego, Calif., assignor to Consolidated Vultee Aircraft Corporation, San Diego, Calif., a corporation of Delaware Application August 20, 1945, Serial No. 611,419:

Claims. 1

The present invention relates to devices for use in testing machine guns as well as the feed of ammunition thereto.

With the advent of a remote firing machine gun which is mounted in a turret or other structure on an airplane and has the cartridge belt fed to it by way of a flexible chute, there has arisen the need or necessity to experiment with the passage of the belt to the gun. Only in this way is it possible to determine how smoothly or satisfactorily the cartridge belt is fed through the feed chute to the gun and where and Why stoppages occur. In the modern airplane machine gun turret with its wide angles of fire much effort has been placed on perfecting smooth feeding feed chutes to insure a constant supply of ammunition to the gun with a minimum amount of pull on the cartridge belt regardless of the angle at which the gun may be fired. In addition to the foregoing it has been necessary to conduct tests or experiments regarding the disposal of the ammunition links and the empty cartridges after the belt passes through the gun. As the cartridges are fired, the ammunition belt, by the action of the ejector mechanism of the gun, is no longer a continuous belt but is broken up into separate links and empty cartridges. The separate links and empty cartridges are ejected rapidly and violently from the gun and either fall into a specially designed container or onto the floor of the turret in which the machine gun is mounted. Unless experiments are made to ascertain what happens to the links and empty cartridges as they are ejected from the gun the possibility exists that the ejected links and cartridges may disable or foul the operating mechanism of the turret or the gun mount at a crucial moment. Heretofore, the aforementioned tests and experiments have made it necessary either to mount the turret with the machine gun therein on a specially built frame and transport it to a suitable firing range or to fly the airplane with the turret to some safe area and there test for all conceivable stoppages and malfunctions. In addition such tests and experiments have required the use of live ammunition and hence have been extremely costly.

The primary object of the invention is to provide a device which will feed dummy ammunition through a machine gun at the guns normal rate of fire to the end that the feed of the cartridge belt to the gun may be tested without firing live ammunition and it is not necessary either to mount the gun turret on a specially built frame or transport the airplane on which the machine gun fi l turret is mounted to a suitable firing range. By providing such a device the feeding of the ammunition or cartridge belt to the gun, the working of the operating parts of the gun, and the ejection of the separate links and cartridges may be observed without the necessity of utilizing or firing live ammunition.

Another object of the invention is to provide a device of the lastmentioned character which is pneumatically operated and serves rapidly and repeatedly to reciprocate or shuttle the bolt of the machine gun to which it is applied.

Another object of the invention is to provide a machine gun testing device of the type and character under consideration, which comprises a cylinder-piston unit the piston of which. is operatively connected to the bolt of the gun.

A further object of the invention. is to provide a testing device of the lastmentioned character in which the cylinder-piston unit is designed to be substituted for the oil buffer body in the receiver of the machine gun and has means whereby it may be attached to the barrel extension of the gun.

A still further object of the invention is to provide a machine gun testing device which is generally of new and improved construction and is characterized by extremely high efficiency of operation and simplicity of design.

Other objects of the invention the various advantages and characteristics of the present machine gun testing device will be apparent from a consideration of the following detailed description.

The invention consists in the several novel features which are hereinafter set forth and are more particularly defined by the claims at the conclusion hereof.

In the drawings which accompany and form a part of this specification or disclosure and in which like numerals of reference denote corresponding parts throughout the several views:

Figure l is a side elevation of a machine gun having applied thereto a testing device embodying one form of the invention, certain parts of the receiver of the gun being broken away or omitted for purposes of illustration;

Figure 2 is an enlarged side view of the testing device of Figure 1, illustrating in detail the manner in which the cylinder-piston unit is attached or connected to the barrel extension of the gun and also the manner in which the piston of the unit is operatively connected to the machine gun bolt;

Figures 3, 4 and 5 are vertical longitudinal sections of the cylinder-piston unit, illustrating in detail the construction design and mode of operation of the various component parts of the unit and showing the manner in which the piston operates in response to reciprocation thereof to actuate or shuttle the bolt of the machine gun;

Figure 6 is a horizontal section on the line -6 of Figure 3;

Figures '7, 8 and 9 are vertical transverse sections taken respectively, on the lines 'l--'l, 8--8 and 9-& of Figure 3; and

Figure 10 is a fragmentary vertical longitudinal section of a machine gun having applied thereto a testing device embodying a second or modified form of the invention.

The testing device which is shown in Figures 1 to 9, inclusive, of the drawings constitutes one form or embodiment of the invention. It is adapted for use in connection with a machine gun ii] and serves as hereinafter described in detail to feed a cartridge belt with dummy cartridges through the gun in order that the feeding of the belt to the gun, the working of the operating parts of the gun, and the ejection of the separate links and cartridges from the gun may be observed without the necessity of utilizing or firing live armunition. The machine gun is is the well known Browning gun which is designed to be mounted in a turret or on any other suitable supporting structure on an airplane and to have the ammunition or cartridge belt fed to it by a flexible chute. In general, the gun comprises a receiver H, a barrel I2, a barrel extension l3, and a bolt M. The receiver l i is horizontally elongated and forms a housing for the barrel extension E3, the bolt 54, and certain other operating parts of the gun. It consists of a pair of laterally spaced side walls i5, a top wall It, a bottom wall ll, and a front wall I3 and has at the rear end thereof a back plate 19. The side walls l5 of the machine gun receiver are spaced apart by the top, bottom and front walls. The front portion of the bottom wall is disposed at a higher elevation than the rear portion and is joined to the latter by a vertically extending cross wall 29. The front wall l8 of the receiver is provided with a collar 2! to which is connected one end of a barrel jacket 22. The back plate I9 is slidably connected to the rear ends of the side walls 55 and has any suitable latch means for releasably securing it in its operative position. The barrel l2 has the front end thereof disposed in the barrel jacket 22 and its rear end positioned within the front portion of the receiver H. The barrel extension i3 is mounted for longitudinal sliding movement in the central portion of the receiver and embodies a pair of laterally spaced sides 24 and a cross wall 25. Said cross wall is connected to, and extends between, the front ends of the sides of the barrel extension and has a socket 26. The rear end of the barrel l2 fits within the socket and is re movably secured in place by means of a screw thread connection 2'1. The rear ends of the sides 24 of the barrel extension are provided with depending extensions 28 which, as well understood in the art, are adapted in connection with the forward sliding movement of the barrel extension to strike against the vertically extending cross wall 28 and thus limit or restrict the forward sliding movement of the barrel extension and the barrel with respect to the receiver H of the machine gun Ill. The bolt I l overlies the barrel extension l3 and is slidably W l lllmmn connected to the latter by way of horizontally extending side ribs which fit within grooves 30 in the inner portions of the sides 24 of the barrel extension. The ammunition or cartridge belt for the machine gun is fed into the receiver through an elongated opening in one of the receiver side walls l5. In connection with normal operation of the machine gun ll) the barrel extension and bolt are forwardly disposed when a cartridge is fired in the barrel i2. As soon as the cartridge ..s fired the force of recoil carries the barrel, the barrel extension and the bolt backwards short distance. This motion serves to unlock the bolt from the barrel extension and the bolt throws back farther toward the back plate [9 against a spring 3!. Rearward movement of the barrel extension and the barrel is checked by way of an oil buffer body (not shown) which is disposed in the rear lower portion of the receiver and extends between the lower end of the back plate 59 and the rear end of the barrel extension l3. During the long rearward motion of the bolt the empty cartridge is withdrawn from the rear end of the barrel. When the bolt is slid or shifted forwards by the spring 3| the empty cartridge case is ejected from the receiver and the next following cartridge is inserted into the rear end of the barrel as well understood in the art.

The testing device which is shown in Figures 1 to 9, inclusive, is designed to be substituted for the oil buffer body which as previously pointed out, is normally disposed in the rear lower portion of the machine gun receiver II. It is operated pneumatically and serves when operated while in its operative position to rapidly and repeatedly reciprocate or shuttle the machine gun bolt it. As its principal parts or components the testing device comprises a horizontally elongated cylinder block 32, a cylinder 33, a piston 3 and a piston rod 35.

The cylinder .lock 32 is formed of any suitable metal and, as shown in the drawings, is rectilinear in cross section. It is shaped and designed to fit within the rear lower portion of the machine gun receiver l l and also to have the front end thereof abut against the rear end of the barrel extension l3 and its rear end abut against the lower end of the back plate IS. The length of the cylinder block is such that when the testing device is in its operative position the block together with the cross wall 20 locks the barrel extension l3 and the barrel I2 against sliding movement relatively to the machine gun receiver ii. The width of the cylinder block corresponds to the width of the receiver interior with the result that the side walls i5 of the receiver hold the cylinder block against sidewise displacement relatively to the receiver. The upper portion of the cylinder block is provided with a cylindrical longitudinally extending open ended bore in which the cylinder 33 is mounted for limited longitudinal sliding movement. The front end of the cylinder block 32 of the testing device is releasably connected to the rear end of the aforementioned barrel extension I3 by a pair of side by side horizontally extending locking keys 37. The rear ends of these keys are provided with enlarged heads 33 and fit in grooves 39 in the front portions of the side bases of the cylinder block. As shown in the drawings the grooves are shaped conformably to the rear ends of the locking keys 31. The front ends of such keys embody depending lugs 40 and fit within correspondingly shaped grooves 4| in the outer faces of the depending extensions at the rear ends of the sides 24 of the barrel extension l3. In

mounting the testing device with respect to the machine gun ID the back plate [3 is first removed from the receiver II by releasing the aforementioned latch means and then sliding it out of connected relation with the rear end of the receiver. moved from the receiver and the barrel extension l3 is'slid rearwards until the rear end thereof is disposed exteriorly of the receiver. After so shifting the barrel extension the front en d of the cylinder block 32 is placed in abutment with the rear end of the barrel extension and the two locking keys 3'! are manipulated in their operative position wherein the rear ends thereof are disposed in the grooves 39 and their front ends are disposed in the grooves 4|. After so positioning the two locking keys the cylinder block 32 is shifted forwards until it is disposed within the rear lower portion of the receiver interior. After this step or operation the back plate 19 of the machine gun is returned to, and latched in, its normal position wherein it closes the rear end of the receiver interior.

The bottom portion of the cylinder block 32 is provided with an L-shaped inlet duct 42 for air under pressure and is also provided with a pair of ,L-shaped discharge ducts 43 and 44. The inlet duct 42 is formed in the rear lower portion of the cylinder block and consists of a longitudinally extending branch 42a and a transversely extending branch 42b at the inner end of the branch 42a. The outer end of the branch 42a has associated with it a fitting 45 whereby a hose or flexible pipe leading from a suitable source of air under pressure may be connected to the inlet duct 42. The receiving end of the fitting 45 extends through a cutout 46 in the back plate l9 of the machine gun and the discharge end of the fitting 'is connected by a screw thread connection 41 to the outer end of a longitudinally extending branch 42a of the inlet duct 42. The transversely extending branch 426 of the inlet duct is located in the central portion of the cylinder block and has the upper portion thereof in intersecting and communicating relation with the central lower portion of the cylindrical open ended bore 36. The discharge duct 43 is formed in the front end of the cylinder block. It consists of a transversely extending branch 43a and a longitudinally extending branch 43b. The branch 43a of the duct 43 is disposed directly forward of, and in parallel relation with, the transversely extending branch 42b of the inlet duct 42 and has the upper portion thereof in intersecting and communicating relation with the central lower portion of the bore 36. The longitudinally extending branch 43?) of the discharge duct 43 leads forward from the outer end of-the transversely extending branch 43a and has the front end thereof in communication with one end of a groove 48 which extends part way around the front portion of the cylindrical longitudinally open ended bore 36 in the upper portion of the cylinder block 32. As shown in the drawings the groove 48 is disposed inward of the front face or extremity of the cylinder block. The other discharge duct, that is, the duct 44, is formed in the rear lower portion of the cylinder block and comprises a transversely extending branch 44a and a longitudinally extending branch 44b.

The branch 44a is disposed directly rearwards of and in parallel relation with, the transversely "extending branch 42b of the inlet duct 42 and has Thereafter the oil buffer body is reits upper portion in intersecting and communicating relation with the lower central portion of the bore 36. The longitudinally extending branch 44b of the discharge duct 44 leads rearwards from the outer end of the branch 44a and has its rear end in communication with one end of a groove 49 around the rear portion of the bore 36. The groove 49 extends part way around the bore and is disposed inward of the rear face or extremity of the cylinder block. i

The cylinder 33 which as previously pointed out is mounted for longitudinal sliding movement in the bore 35 in the cylinder block 32 is tubular in design and has a cylinder head 50 at the front end thereof and a cylinder head 5| at its rear end. The head 56 is provided with a centrally positioned bore 52 and is secured in place by way of a screw thread connection 53. A spiral compression spring 54 is suitably mounted on the inner end face of the cylinder head 59 and extends concentrically around the centrally disposed bore 52. A port 55 is formed in the front end of the cylinder and this is disposed directly inward of the cylinder. head 50 and is in registry with the groove 48 that communicates with the front end of the longitudinally extending branch 43b of the discharge duct 43. The cylinder head 5| is imperforate. It serves to close or seal the rear end of the interior of the cylinder 33 and is secured in place by .a screw thread connection 56. A spiral or helical compression spring 51 is mounted on the central portion of the inner face of the cylinder head 5|. The rear end of the cylinder 33 is provided with a port 58 and this is disposed directly in front of the cylinder head 5| and registers with the groove 49 which as heretofore described communicates with the rear or outer end of the longitudinally extending branch 44b of the discharge duct 44. Longitudinal sliding movement of the cylinder 33 with respect to the cylinder block 32 is limited by way of a connection in the form of a groove 59 and a pin 60. The groove 53 is formed in, and extends longitudinally of, the bottom portionof the cylinder 33. The pin 63 extends upward through the bottom portion of the cylinder block and has its upper end disposed in the groove 53. The cylinder is of such length that when it is slid or shifted forward to its fullest extent as shown in Figure 4 the front end of the cylinder is disposed outward of and seals from atmosphere the groove 48, the port 55 is disposed opposite to the outer or front portion of the groove 48, the rear end of the cylinder is disposed adjacent the central portion of the groove 43, and the port 58 is positioned opposite the front or inner portion of the groove 49. Vthen the cylinder is shifted rearwards to its fullest extent as shown in Figure 5 the rear end of the cylinder is disposed outwards of and seals from atmosphere the groove 49, the front end of the cylinder is disposed adjacent the central portion of the groove 48, and the port 55 is positioned opposite the inner portion of the groove 48. The central lower portion of the cylinder 33 is provided with a cutout Bl which when the cylinder is shifted forwards to its fullest extent, bridges and establishes communication between the transversely extending branches 42b and 43a of the ducts 4E and 43 and when the cylinder is shifted or slid rearthe front end of the cylinder 33 by way of the inlet duct 42, the cutout 65, the discharge duct 43,'the groove 48, and the port 55, and the rear end of the cylinder is vented by way of the port 58 and the groove 49. When the cylinder is shifted or slid rearwards the rear end of the cylinder is supplied with air under pressure by way of the inlet duct 42, the cutout the discharge duct 44, the groove do and the port 53, and the front end of the cylinder is vented by way of the ports 55 and the groove 43.

The piston 34 is mounted in the cylinder 33! to slide or reciprocate back and forth between the cylinder heads 5i and 51. The piston rod 35 extends slidably through the centrally disposed bore 52 in the cylinder head 56 and has the rear end thereof fixedly connected to the central'portion of the piston 34. The front end of the piston rod is disposed between the sides .24 of the machine gun barrel extension is and has its forward extremity operatively connected to the front end of the bolt l4 by way of an upstanding arm 62. As shown in the drawings, the lower end of the arm 62 is fixedly connected to the adjacent end of the piston rod and the upper end of the arm is shaped to fit snugly within a socket 63 in the front end of the bolt 14. As a result of the connection between the front end of the piston rod and the front end of the bolt, the bolt is caused to move back and forth for cartridge belt feeding purposes in response to reciprocation of the piston 34 in the cylinder 33. When the cylinder and piston are positioned as shown in Figure 4, air under pressure enters the front end of the cylinder as hereinbefore pointed out and causes the piston 34 together with the piston rod 35 and the machine gun belt I 4 to slide rearwards. During rearward sliding movement of the piston the air in the rear end of the cylinder is exhausted to atv mosphere via the ports 58 and the groove 49. As soon as the piston reaches the end of its rearward stroke it strikes against the compression spring 51 with such force that the cylinder 33 is caused to slide rearwards relatively to the cylinder block 32. Rearward sliding of the cylinder is directly attributable to the fact that the piston slides rearwards at an extremely rapid rate and strikes the spring ill with considerable force due to the momentum of the piston, the piston rod, and the machine gun bolt. .As soon as the cylinder is shifted rearwards so as to cause the cutout iii to bridge and establish communication between the branches 42b and 44a of the ducts 42 and 44 air under pressure enters the rearj end of the cylinder and causes the piston together with the piston rod and the machine gun bolt to slide forwards. During forward sliding movement of the piston the front end of the cylinder is vented via the port 55 and the groove 43. As soon as the piston reaches the end of its forward stroke it strikes against the compression spring 5 1 and shifts the cylinder forwards into a position wherein the aforementioned cycle again takes place. The speed or rapidity of reciprocation of the piston its is dependent upon the pressure of the air which enters the cylinder through the

ports

55 and 58. It is contemplated that in normal use of the testing device the pressure of the air wil be such that the piston will reciprocate at a speed correspending to the machine guns normal rate of fire. The compression springs 5d and 5? serve to separate the piston from the cylinder heads when the piston reaches the ends of its strokes and thus assure admission of air under pressure into the cylinder.

In using the testing device of Figures 1 to 9, inclusive, the device is manipulated into its operative position wherein as previously pointed out it serves as a substitute for the oil buffer body in the rear lower portion of the interior of the machine gun receiver II. In connection with manipulation of the device into place the upper end of the arm 62 is inserted into the socket 63 in the front end of the bolt l4 before the barrel extension 53 and the cylinder block 32 are slid into the receiver. When it is desired to utilize the testing device it is only necessary to supply air under pressure to the fitting 45. As soon as the flow of air under pressure to the fitting commences, the piston 34 is rapidly reciprocated and operates through the medium of the piston rod 35 to cause the machine gun bolt Hi to slide or shuttle back or forth. Such movement on the part of the bolt results in the cartridge belt being fed through the gun. By employing the testing device dummy ammunition may be fed through the machine gun to the end that the feed of the belt through the flexible chute leading to the receiver of the gun, the working of the operating parts of the gun, and the ejection of the separate links and cartridges from the receiver may be observed without the necessity of utilizing or firing live amxnunition.

The testing device of Figures 1 to 9, inclusive, effectively and efiiciently fulfills its intended purpose and is characterized by the fact that it may be manufactured and operated. at a low cost and in addition may be mounted and removed with facility. It is essentially a substitute uni for the regular oil buffer body of the machine gun and makes it possible to test the machine gun and the feed of ammunition thereto without the necessity of either mounting the turret for the gun on a specially built frame and transporting it to a suitable firing ran e or fiying or transporting the airplane with the turret to a safe firing area. In addition to serving as a medium or instrumentality for testing a machine gun and the feed of ammunition thereto, the device may be utilized to give a permanent set to the mount for the machine gun. In such case no ammunition belt is fed to the machine gun receiver and the device as the result of the rapid reciprocation of the bolt produces a hammering action which simulates the normal hammering action resulting from firing of the gun and imparts the desired permanent set to the machine gun mount.

The testing device which is shown in Figure 19 constitutes a second or modified embodiment of the invention. It functions similarly to, and serves the same purpose as, the machine gun testing device of Figures 1 to 9, inclusive, but diil'ers therefrom in that it is in the form of a unitary structure which is adapted to be substituted for the barrel, the barrel extension and the bolt of the machine gun to which it is applied. As its component parts the subject testin device comprises a unit 64, a barrel extension 85, and a bolt 66. The unit 64 includes a cylinder block 53, cylinder 615, a piston 65), and a piston rod l5) and is the same as the testing device of Figures 1 to inclusive, except that the front end of the cylinder block 67, instead of being detachably connected to the rear end of the barrel extension, is formed integrally with the barrel extension. The bolt 66 is slidably con- I collar rearwards.

the end of its rearward stroke.

portion of the back plate.

nected to the barrel extension 65 and has its front end operatively connected to the front end of the piston rod 18 by an upstanding arm H the lower end of which is fixedly connected to the piston rod and the upper end of which fits within a socket in the front end of the bolt 65. The testing device of Figure 10 includes no conventional barrel on the front end of the barrel extension 65. It does, however, include a sleeve 12 in lieu of a barrel. This sleeve is located directly in front of the extension barrel 65 and has a centrally apertured screw plug 13 in its front end. The aperture in the plug is adapted to receive the cartridges in connection with a machine gun testing operation. The rear end of the sleeve 12 fits within the centrally disposed socket in the vertically extending cross Wall of the barrel extension, is connected thereto by a screw thread connection 14, and has an integral inwardly extending flange i5. An abutment collar 16 is arranged in associated relation with the rear end of the sleeve '82. This collar is positioned concentrically with respect to the sleeve and has at its front end an angular outwardly extending flange H which fits slidably within the rear end of the sleeve and coacts with the inwardly extending flange T to limit rearward sliding movement of the collar with respect to the sleeve. A rectilinear series of pairs of opposed conical or dome shaped spring washers-18 extends between the plug 13 and the outwardly extending flange '11 on the front end of the abutment collar 76 and serves to urge the The length of the collar '55 is such that in connection with forward sliding of the bolt 66 by the piston 69 the collar is engaged by the front end of the bolt and urged forwards against the force of the spring washers 18. Upon release or expansion of the washers the collar moves rearwards substantially instantaneously and imparts rearward sliding movement -to the bolt 66. Such rearward sliding movement on the part of the bolt moves the piston 69 of the unit 64 away from the cylinder head at the front end of the cylinder 68. The spring action which is occasioned or produced by the spring washers 18 tends to cause the unit 64 to operate at an extremely high rate of speed and eliminates the necessity of providing a spiral or helical compression spring on the inner face of the cylinder head at the front end of the cylinder 68.

It is contemplated that when the testing device of Figure is used for machine gun testing purposes a special back plate l9 will be utilized instead of the regular or conventional back plate on the rear end of the machine gun receiver. The back plate 19' is like the standard or conventional back' plate except that it includes a spring assembly 86 which imparts a quick acting forward force to the bolt 65 when the latter reaches This spring assembly 80 functions in the same manner as the spring assembly consisting of the sleeve 12, the plug 13, the abutment collar and the spring Washers I8 and comprises as its parts a sleeve BI, a plug 82, an abutment collar 83, and a rectilinear series of pairs of opposed conical or dished spring washers 8d. The sleeve 8! is in registry with and extends rearwards from an aperture 85in the back plate 19 and has the front end thereof fixedly secured to the aperture defining The plug 82 fits within the rear end of the sleeve 8! and is adjustably secured thereto by way of a screw thread connection 86. The front end of the sleeve 8i is provided with an integral inwardly extending flange 81. The abutment collar 83 is located adjacent the front end of the sleeve 8| and embodies an outwardly extending angular flange which fits slidably within the front end of the sleeve and coacts with the flange ti to limit or restrict forward sliding movement of the abutment collar with respect to the sleeve. The washers 86 are interposed between. the plug 82 and the rear end of the abutment collar 83. Said collar is of such length and so positioned that it is engaged and shifted rearwards by the bolt (56 at the endiof the rearward stroke of the bolt. When the bolt reaches the end of its rearward stroke it shifts the abutment collar 83 rearwards against the force of the spring washers 84. When the washers recover their normal position they shift the abutment collar 83 forwards substantially instantaneously and impart forward movement to the bolt 65. The spring assembly Bil constitutes a recoil medium for imparting forward movement to the bolt at the end of the latters rearward stroke, increases the speed of action of the unit (it and eliminates the necessity of mounting a compression spring on theinner face of the cylinder head at the rear end of the cylinder 68.

When it is desired to use the testing device of Figure 10 for machine gun testing purposes the regular back plate of the gun is first removed. Thereafter the oil bufier body, the barrel extension, the barrel, and the bolt of the gun are removed through the open rear end of the machine gun receiver. Upon removal of these parts of the gun the testing device is shifted into the receiver and is then secured in place by sliding the special back plate 19 into interfitting relation with the rear end of the gun receiver. When it is desired to operate the device air under pressure is supplied to the cylinder block 61 of the unit 54. As soon as air under pressure is supplied to the cylinder block the piston 69 is rapidly reciprccated and efiects corresponding reciprocation of the bolt 66. The bolt 66 is provided with no firing mechanism with the result that when it is reciprocated in connection'with feed of a cartridge belt through the receiver of the machine gun there is no firing of the cartridges even though the cartridges forming a part of the belt are in the form of live ammunition. After the testing device of Figure 10 has served its purpose it may be removed merely by removing the back plate 79 and sliding the device bodily out of the open rear end of the receiver of the machine gun.

The testing device of Figure 10 like the device of Figures 1 to 9, inclusive, effectively and efiiciently fulfills its intended purpose andis charac terized by the fact that it is extremely quick acting and will feed a cartridge belt at high speed through the receiver of the gun with which the device is used. It is comparatively simple in design and may be installed and removed with facility.

The invention is not to be understood as restricted to the details set forth since these may be modified within the scope of the appended claims without departing from the spirit and scope of the invention.

Having thus described the invention, what I claim as new and desire to secure by Letters Patent is:

l. A device designed for use in testing a machine gun of the type that embodies a receiver, a barrel extension and a removable bufier unit in the receiver, and a cartridge feeding bolt slidably connected to the barrel extension, and comprising a housing adapted to be mounted in the receiver in place of the buffer unit and having a cylinder therein, a piston mounted slidably in the cylinder, provided with means for operatively connecting it to the bolt and adapted when reciprocated to shuttle the bolt, and means for alternately supplying air under pressure to opposite ends of the cylinder in order to effect reciprocation of the piston.

2. A device designed for use in testing a machine gun of the type that embodies a receiver, a barrel extension disposed in the receiver and, including a pair of laterally spaced sides, a bufier unit mounted in the receiver behind the barrel extension, and a cartridge feeding bolt connected to the barrel extension so that it is slidable lengthwise of the receiver, said device comprising a housing adapted to fit removably in the receiver behind the barrel extension after removal of the buffer unit and having a, cylinder therein extending lengthwise of the receiver, a piston slidably mounted in the cylinder, a piston rod connected to, and extending forwards from, the piston, having the front end thereof positioned between the sides of the barrel extension and provided with means for connection to the bolt, and adapted in response to reciprocation of the piston to shuttle the bolt for cartridge feeding purposes, and means for alternately supplying air under pressure to opposite ends of the cylinder in order to effect reciprocation of the piston.

3. A device designed for use in testing a ma-- chine gun of the type that embodies a receiver with a removable back plate, a barrel extension in the central portion of the receiver, a bufier unit in the receiver between the barrel extension and the back plate, and a cartridge feeding bolt connected to the barrel extension so that it is slidable lengthwise of the receiver, said device comprising a housing shaped and adapted to fit removably in the receiver between the barrel extension and the back plate after removal of the buffer unit and having a cylinder extending lengthwise of the receiver, a piston slidably mounted in the cylinder, provided with means for operatively connecting it to the bolt, and adapted when reciprocated to shuttle the bolt for cartridge feeding purposes, and means for alternately supplying air under pressure to opposite ends of the cylinder in order to effect reciprocation of the piston.

4. A device designed for use in testing a machine gun of the type that embodies a receiver With a removable back plate, a barrel extension mounted in the central portion of the receiver for limited forward and rearward sliding movement, a buffer unit disposed in the receiver between the barrel extension and the back plate, and a bolt positioned above the barrel extension and connected thereto so that it is slidable lengthwise of the receiver, said device comprising a housing shaped and adapted to fit removably in the receiver between the barrel extension and the back plate after removal of the buffer unit, adapted when in place to lock the barrel extension against sliding movement, and having a cylinder therein extending lengthwise of the receiver, a piston slidably mounted in the cylinder, a piston rod having one end thereof connected to the piston and its other end provided with means for connection to the bolt, and adapted in response to reciprocation oi the piston to shuttle the bolt for cartridge feeding purposes, and means for alternately supplying air under pressure to pl2 posite ends of the cylinder in order to effect reciprocation of the piston.

5. A device designed for use in testing amachine gun of the type that embodies a receiver with a removable back plate, a barrel extension mounted in the central portion of the receiver for limited forward and rearward sliding movement and including a pair of laterally spaced sides, a buffer unit disposed in the receiver between the barrel extension and the back plate, and a cartridge feeding bolt positioned above the barrel extension and connected thereto so that it is slidable lengthwise of the receiver, said device comprising a housing shaped to fit removably in the receiver between the barrel extension and the back plate after removal of the buffer unit, adapted when in place to lock the barrel extension against sliding movement, and having a cylinder therein extending lengthwise of the receiver, a piston slidably mounted in the cylinder, a piston rod connected to, and extending forwards from, the piston, having the front end thereof positioned between the sides of the barrel extension and provided with means for connec tion. to the bolt, and adapted in response to reciprocation oi the piston to shuttle the bolt, and means for alternately supplying air under pressure to opposite ends of the cylinder in order to effect reciprocation of the piston.

6. A device designed for use in testing a machine gun of the type that embodies a receiver, a barrel extension disposed in the receiver and provided with a slidable breech lock, a buffer unit mounted in the receiver behind the barrel extension, and a cartridge feeding bolt connected to the barrel extension so that it is slidable lengthwise of the receiver and adapted when slid forwards to be locked by the breech lock, said device comprising a housing adapted to be mounted in the receiver in place of the bufier unit, provided with means for connecting it to the barrel extension and having a cylinder therein, a. piston slidably mounted in the cylinder, provided with means for operatively connecting it to the bolt and adapted when reciprocated to shuttle the bolt, and means for alternately supplying air under pressure to opposite ends of the cylinder in order to eiiect reciprocation of the piston.

'7. A device designed for use in testing a machine gun of the type that embodies the receiver, a barrel extension disposed in the central portion of the receiver, provided with a slidable breech look, and including a pair of laterally spaced sides, a buffer unit removably mounted in the receiver behind the barrel extension, and a cartridge feeding bolt connected to the barrel extension so that it is slidable lengthwise of the receiver and adapted when slid forwards to be locked by the breech lock, said device comprising a housing adapted to be mounted in the receiver behind the barrel extension after removal of the buffer unit, provided at the front end thereof with means for connecting it to the barrel extension, and having a cylinder therein extending lengthwise of the receiver, a piston slidably mounted in the cylinder, a piston rod connected to, and extending forwards from, the piston, having the front end thereof adapted for disposition between the sides of the barrel extension and provided with means for connection to the bolt, and adapted in response to reciprocation of the piston to shuttle the bolt for cartridge feeding purposes, and means for alternately supplying air under pressure to opposite ends of the cylinder in order to effect reciprocation of the piston.

8. A device designed for use in testing a ma- 13 chine gun of the type that embodies a receiver with a removable back plate, a barrel extension mounted in the central portion of the receiver for limited forward and rearward sliding movement, provided at its rear end with a slidable breech lock, and including a pair of laterally spaced sides, a bufier unit disposed in the receiver between the barrel extension and the back plate, and a cartridge feeding bolt connected to the barrel extension so that it is slidable lengthwise of the receiver and adapted when slid forwards to be locked by the breech lock, said device comprising a housing adapted to be mounted in the receiver between the barrel extension and the back plate in place of the bufier unit, adapted when in place to lock the barrel extension against sliding movement, provided with means at its front end for connecting it to the barrel extension, and having a cylinder therein extending lengthwise of the receiver, a piston slidably mounted in the cylinder, a piston rod connected to, and extending forwards from, the piston, having the front end thereof adapted for disposition between the sides of the barrel extension and provided with means for connection to the bolt and adapted in response to reciprocation of the piston to shuttle the bolt, and means for alternately supplying air under pressure to opposite ends of the cylinder in order to effect reciprocation of the piston.

9. A device for use in testing a machine gun of the type that embodies a receiver, a barrel extension and a buffer unit in the receiver, and a cartridge feeding bolt mounted to slide relatively to the barrel extension, said device being 14 designed to be mounted in the receiver in place of the buffer unit and embodying a power actuated unit having means for operatively connecting it to the bolt and adapted when actuated to shuttle the bolt.

10. A device adapted for use in testing a machine gun of th type that embodies a receiver, a barrel extension and a buffer unit in the receiver, and a cartridge feeding bolt mounted to slide relatively to the barrel extension, said device being designed to be mounted in the receiver in place of the bufier unit and embodying a pneumatically actuated cylinder-piston unit having means for operatively connecting it to the bolt and adapted when actuated to shuttle the bolt.

GLEN E. MCPHERREN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS OTHER REFERENCES Publication, Tine-225 War Dept., December 15, 1943, Browning Machine Gun Cal. 50 M2, Aircraft Basic. v