US 3641869 A
In an automatic gun wherein the headspace varies with the thermal elongation of the barrel during firing operation, the barrel chamber is provided with at least three control pins which are disposed parallel to the longitudinal axis of the chamber so as to act simultaneously upon the rim of the chambered cartridge to compensate by indentation of the rim for the variations in headspace and assure positive zero space between the cartridge and breechblock throughout the range of headspace variations and greater than zero space between the barrel and breechblock when the gun is in battery.
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Description (OCR text may contain errors)
United States Buchanan et al.
[ Feb. 15, 1972 iord E. La Fever, Mission Viejo, both of Calif.
 Assignee: The United States of America as represented by the Secretary of the Army  Filed: June 9, 1970  Appl. No.: 44,837
 US. Cl ..89/14 R, 42/1 0  Int. Cl. ..F4lc 21/12, F4lf 17/00  Field ofSearch ..42/1 Q, 76 R, 10, l1;89/14 R, 89/16, 161
 References Cited UNITED STATES PATENTS 2,645,160 7/1953 Gilligan ..42/1 0 3,411,405 11/1968 Pachmayr et al. ..42/] Q Primary Examiner-Benjamin A. Borchelt Assistant ExaminerC. T. J ordan Attorney-Edward J. Kelly, Herbert Berl, Harry M. Saragovitz and Albert E. Arnold, Jr.
 ABSTRACT In an automatic gun wherein the headspace varies with the thermal elongation of the barrel during firing operation, the barrel chamber is provided with at least three control pins which are disposed parallel to the longitudinal axis of the chamber so as to act simultaneously upon the rim of the chambered cartridge to compensate by indentation of the rim for the variations in headspace and assure positive zero space between the cartridge and breechblock throughout the range of headspace variations and greater than zero space between the barrel and breechblock when the gun is in battery.
6 Claims, 6 Drawing Figures CARTRIDGE CHAMBER STRUCTURE TO COMPENSATE FOR VARIABLE HEADSPACE BACKGROUND OF THE INVENTION This invention relates to gun barrels and pertains more particularly to the structure of the cartridge chamber therein.
In automatic guns wherein the barrel is reciprocated between fixed forward and rearward positions by mechanical means connecting an external actuating means to the barrel intermediate the length thereof, trouble is frequently experienced in the operation of the gun as a result of the thermal elongation of the barrel between the breech end and the area thereof at which connection is made to the external actuating means. i
The elongation varies the gun headspace between the front face of the breechblock where contacted by the base of the chambered cartridge and the area in the chamber which controls the forward position of the cartridge therein for discharge and is critical in the operation of the gun. Difficulty has been experienced in overcoming the problems which are inherent in such a variable headspace because when the headspace is designed great enough to prevent jamming contact between the barrel breech and the breechblock when the barrel is elongated by firing it becomes so great when the barrel is at ambient temperature that the firing pin is not always effective against the cartridge primer for detonation thereof. The contrary is also true. When the headspace is designed to assure positive contact between the firing pin and cartridge primer when the barrel is at ambient temperature then jamming contact between the barrel and breechblock is experienced when the barrel is at operating temperature.
SUMMARY OF THE INVENTION Considerable effort has been made to design for such guns a mean headspace such as would assure trouble free operation throughout the full range of the headspace variations but without success. The present invention overcomes this problem, however, by providing for the barrels of such guns cartridge chamber structure which acts against the cartridge rim to compensate for the thermal elongation of the barrel and assure zero space between the base of the chambered cartridge and the breechblock at all the variations in the headspace resulting from the thermal elongation of the barrel, and a space greater than zero between the barrel breech and the breechblock when the gun is in battery.
To accomplish this, it is a principal object of this invention to provide chamber structure which will permit variable accommodation of the cartridge in the chamber within a range at least equal to the extent of the variable headspace.
It is still another object of this invention to provide for such gun barrels other chamber structure comprising at least three control pins mounted in the chamber parallel to the central axis thereof so as to act simultaneously against the rim of the chambered cartridge for deformation thereof to provide rim structure which cooperates with the pins in controlling the forward position of the cartridge and assure that the base thereof is firmly held against the breechblock when the barrel is in battery position.
Further objects and advantages of the invention will be apparent from the following specification and the accompanying drawings which are for the purpose of illustration only.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a fragmentary, longitudinally cross-sectioned view of an automatic gun comprising a barrel which is reciprocate'd between fixed forward and rearward positions by rotary cam means;
FIG. 2 is an enlarged, cross-sectional view taken along line 22 of FIG. 1;
FIG. 3 is a cross-sectional view taken along line 3-3 of FIG. 2 but shows the chambered cartridge positioned with zero spacing from the breechblock by the ends of the control pins when the barrel is of ambient temperature;
FIG. 4 is a view similar to FIG. 3 but shows the chambered cartridge held firmly against the breechblock through the cooperation of the ends of the control pins with deformations produced thereby in the cartridge rim when the thermal elongation of the barrel is between the maximum and minimum limits thereof;
FIG. 5 is a view similar to FIGS. 3 and 4 but shows the barrel at the maximum limit of the thermal expansion thereof; and
FIG. 6 is a reduced, perspective view of the cartridge rim as indented by the control pins in FIG. 5.
Shown in the FIGURES is an automatic gun 12 for firing a cartridge 14 comprising a case 16 having a base 18 which forms a circumferential rim 20 with a front edge 22 of conical configuration. Gun 12 comprises a barrel 24 which is reciprocated between a forward and a rearward position by a rotary drum 26 provided with an endless cam groove 28 around the circumference thereof and such cam groove is engaged by a cam follower 30 fixed to barrel 24, intermediate the length thereof, for translating rotation of the drum to longitudinal displacement of the barrel.
A feeding mechanism (not shown) delivers cartridge 14 between breechblock 32 and barrel 24 for envelopment thereby when going into its rearward position. At the same time, base 18 of cartridge 14 is seated in a cylindrical recess 34 with a seating surface 36 in breechblock 32 so that a firing pin 38 carried thereby is actuatable against primer 40 in cartridge 14 for detonation thereof. When barrel 24 is of ambient temperature and is located in its rearward position, breechblock 32 and the barrel are so related that rear face 42 thereof is spaced from the front face 43 of the breechblock a distance xx, as noted in FIG. 3, which is at least equal to the distance which the rear face will be displaced towards the breechblock by the thermal elongation of the barrel between the rear face thereof and cam follower 30 under maximum firing conditions.
A chamber 44 formed in the rear end of barrel 24 receives cartridge 14 when enveloped thereby and such chamber is counterbored from rear face 42 to a shoulder 46 to provide a clearance 48 for receiving rim 20. Shoulder 46 is conically formed to conform to front edge 22 of rim 20. The depth of clearance 48 is at least equal to distance xx, as will be explained hereinafter.
Three holes 50 which have their axes in the circumference of clearance 48 extend into barrel 24 from rear face 42 parallel to the central axis of chamber 44 and such holes are spaced equally apart therearound as shown in FIG. 2. Inserted into each of the holes 50, and fixed therein by conventional means, is a pin 52 having a free end 54 which is spherically formed. Pins 52 are located in holes 50 so that ends 54 touch upon a plane which includes rear face 42, and as the axes of the holes lie in the circumference of clearance 48 a semicylindrical portion of each of the pins protrudes thereinto, as shown in FIGS. 3, 4 and 5.
When barrel 24 is of ambient temperature and the variable headspace is at the maximum limits thereof, as shown in FIG. 3, chamber 44 and seating surface 36 of recess 34 in breechblock 32 are so related that front edge 22 of cartridge 14, when located in the chamber, contacts ends 54 of pins 52 to control the forward position of the cartridge in the chamber so as to effect zero space between base 18 of the cartridge and such seating surface when the barrel is in its rearward position. Thus, impact between firing pin 38, when released, and primer 40 is assured. As the temperature of barrel 24 increases with the firing of cartridge 14 therein, rear face 42 of the barrel is displaced rearwardly relative to cam follower 30 and closer to breechblock 32 by thermal expansion of the barrel so that as the barrel goes into its rearward position pins 52 indent rim 20 of the chambered cartridge to a depth corresponding to the elongation of the barrel and form indentations 56 which are terminated by end walls 58 which cooperate with ends 54 in controlling the forward position of cartridge 14 in chamber 44 so as to effect zero space between base 18 of the cartridge and seating surface 36. When barrel 24 reaches maximum thermal elongation, shoulder 46 in chamber 44 contacts rim of cartridge 14 to locate the forward position thereof in chamber 44.
Thus, chamber 44 is seen to comprise structure which compensates for the full range of variations in the headspace of gun 12. When barrel 24 is of ambient temperature, ends 54 are contactable by rim 20 of cartridge 14 to locate the forward position thereof in chamber 44 and, when the barrel is of maximum operating temperature, shoulder 46 is contactable by the rim to locate the forward position of the cartridge in the chamber. When the temperature of barrel24 is between these limits, pins 52 form cooperating structure in rim 20 which compensate for the resulting thermal elongation to assure zero space between base 18 of cartridge 14 and seating surface 36 in breechblock 32.
We wish it to be understood that we do not desire to be limited to the exact details of construction shown and described, for obvious modifications will occur to a person skilled in the art.
1. In an automatic gun for firing a cartridge having a base and a circumferential rim therearound, said gun comprising a breechblock and a barrel connected intermediate the length thereof to external means for reciprocation thereby between a forward position and a rearward position enveloping said cartridge, said breechblock and said barrel, when in the rearward position, defining a variable headspace responsive to thermal elongation of said barrel, the improvement comprising in said barrel a cartridge chamber including means cooperating with said cartridge to compensate for variations in the headspace and effect zero space between said base and said breechblock and a space greater than zero between said barrel and said breechblock when said barrel is in the rearward position.
2. The invention as defined in claim 1 and wherein said cooperating means comprises a recess in said chamber for receiving said rim, said recess being dimensioned to provide for displacement of said rim relative to said chamber a distance at least equal to the displacement of said chamber relative to said breechblock by thermal elongation of said barrel.
3. The invention as defined in claim 2 and wherein said cooperating means includes means extended into said recess for engaging said rim thereby to control the forward position of said cartridge in said chamber by maintaining said base in zero space relationship with said breechblock.
4. The invention as defined in claim 3 and wherein said extension means comprises at least one pin disposed in said barrel to extend radially into said chamber recess and parallel to the central axis thereof whereby an indentation is formed in said rim according to the thermal elongation of said barrel when said barrel is moved into the rearward position.
5. The invention as defined in claim 4 and wherein said pin comprises a terminal free end of spherical configuration disposed coextensive with a plane including the rear face of said barrel and to contact a front edge of said rim when said barrel is of ambient temperature and is in the rearward position.
6. The invention as defined in claim 5 and wherein said indentation comprises a terminating end wall formed by said free end when thermal elongation of said barrel is between maximum and minimum limits thereof, and said end wall cooperates with said free end to control the forward position of said cartridge in said chamber according to the headspace effected by the thermal elongation of said barrel.