US3040662A

US3040662A - Bullets

Info

Publication number: US3040662A
Application number: US854209A
Authority: US
Inventors: William A Zisman; Simmons Vincent G Fitz
Original assignee: Individual
Current assignee: Individual
Priority date: 1959-11-19
Filing date: 1959-11-19
Publication date: 1962-06-26
Anticipated expiration: 1979-06-26

Description

June 1962 w, A. ZISMAN ETAL 3,040,652

BULLETS Filed Nov. 19, 1959 2 LEAD lNTERED POLYMER WASHER INVENTOR5 WILLIAM A. ZISMAN VINCENT e. FITZSIMMONS ATTORNEY United States Patent BULLETS William A. Zisman, Silver Spring, Md., and Vincent G. Fitz Simmons, McLean, Va., assignors to the United States of America as represented by the Secretary of the Navy Filed Nov. 19, 1959, Ser. No. 854,209

2 Claims. (Cl. 102-93) (Granted under Title 35, US. Code (1952), see. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates to ammunition, more particularly to an improvement in projectiles of low melting point metal which is designed to increase the firing life of gun barrels.

This application is a continuation-in-part of our application, Serial No. 480,624, filed January 7, 1955 now US. Patent No. 2,928,348.

Metal fouling, if unchecked, will eventually terminate the firing life of gun barrels. It is caused by the deposition of softer metal from the projectiles on to the rifiing of the gun during firing and by accumulation produces a roughened surface on the rifiing which is reflected in deviations in the spin imparted to the projectile and there'- by loss in accuracy in the gun fire. Loss in muzzle velocity of the projectile may also result from metal fouling.

We have found that the firing life of gun barrels can be materially increased by so modifying the projectile of low melting point metal that the portion of its surface which normally makes contact with the rifiing of the gun on firing is in part essentially sintered polytetrafluoroethylene. Polytetrafluoroethylene is a polymer known in the trade as Teflon. By so modifying the projectile, there eventuates, on firing of the gun, a system of contact between the projectile and the rifiing which is not metalto-metal but polymer-to-polymer. This flows from the fact that sintered polymer is transferred from the projectile to the rifiing by rubbing to form on the latter a thin coating or film of the sintered polymer. The coating on the rifiing does not build up by accumulation to an undesirable degree of thickness due to the non-self-adhering property of the sintered polymer, the thickness of the coating being that of the thin film as initially applied by the transfer from the projectile. When breaks occur in the film, renewal of the open portions is effected in the same manner; the exposed metal portions of the rifiing receiving sintered polymer by transfer from the subsequently fired projectile. A reverse arrangement in which the rifiing is coated with sintered polymer and the projectiles are of the usual construction is impractical since movement of the projectile over the rifiing will remove portions of the coating until eventually it is worn oif.

Among the beneficial results flowing from the presence of the sintered polymer on or as that portion of the surface of the projectile which contacts the rifiing of the gun, is the absence of metal fouling. Another beneficial result is reduction in the rate of wear of the gun barrel by friction, the sintered polymer having a low coefficient of friction. A further beneficial result and one of importance to rapid fire guns, especially those which are automatic, is reduction in the occurrence of heat erosion of the gun barrel. The sintered polymer has a low thermal conductivity and this property in the polymer film on the rifiing serves to delay transfer of heat from the hot, high temperature gases to the metal of the surface of the gun bore and by consequence, promotes discharge of a greater portion of the heat from the gun barrel by "ice Another beneficial result is a greater from firing debris in the gun barrel, the sintered polymer surface on the projectile having the remarkable property of cleaning the gun barrel. Still another beneficial result is a tendency to give a greater muzzle velocity for the projectile. Yet another beneficial result is elimination of the need of oiling the projectile with consequent avoidance of pick-up of dust and sand by the oil.

Projectiles of low melting point metal, e.g., a lead bullet, are modified in accordance with the invention by making a preformed insert of essentially sintered polytetrafluoroethylene an integral part of the projectile. The insert in the form of a ring or washer is inset in the periphery of the projectile to form part of the surface which normally contacts the rifiing of the gun and with the low melting point metal forms a unitary, one-piece structure.

Modification of the projectiles in accordance with the invention is illustrated in the single figure of the accompanying drawing which forms part of the description of the invention.

In the drawing:

The single FIGURE shows a small arms projectile of low melting point metal modified in accordance with the invention through the inclusion of an insert of sintered polytetrafluoroethylene, the periphery of which forms part of the surface of the projectile.

Referring to the single figure of the drawing, the projectile l of low melting point metal is a lead bullet which contains as an integral part thereof, a washer 2 of sintered polytetrafluoroethylene. A coating of the sintered polymer cannot be successfully applied to low melting point metals because of the high temperature necessary for sintering of the polymer. The washer 2 is located in the bullet behind the ogive and is conterminous with the adjacent or bearing surface of the bullet. A suitable thickness of the sintered polymer washer 2 is on the order of .025 inch for all small arms bullets, regardless of caliber. As illustrated, the composite bullet of the invention is for a .30 caliber rifle.

The new composite bullets may be made by casting in bullet molds in the usual way with the modification that the washer 2 of the sintered polymer is previously placed in the predetermined position in the mold cavity. The hole in the washer 2 of sintered polymer should be large enough to allow the molten, low melting point metal, such as lead or one of the usual lead alloys, to flow through and fill the bottom as well as the upper portion of the bullet mold cavity, whereby on cooling the casting embraces the washer of sintered polymer as an integral part of the bullet. The washer 2 can be formed by cutting from a tape of the sintered polymer of the required thickness, the outer diameter of the washer being that of the bullet. The washer is dropped into the mold cavity to lie in a horizontal position and is located at the proper level by virtue of the convergence of the walls of the mold cavity which are tapered to form the ogive of the bullet.

Instead of the use of convergence of the walls of the mold cavity to determine the position of the washer of sintered polymer in the bullet, one may employ a Washer of a diameter which is but very slightly greater than the inside diameter of the mold cavity and push this slightly oversize diameter washer into the section of the mold cavity which defines the bearing portion of the bullet to the desired depth, whereby selected positioning of the sintered polymer ring in the bearing surface of the bullet may be had.

Since the invention described herein may be variously practiced without departing from the spirit and scope thereof, it is not intended that it be limited except as is required by the appended claims.

way of the muzzle. degree of freedom What is claimed is:

1. An elongated bullet of low melting point metal selected from the group consisting of lead and lead alloys, said bullet being adapted to be fired from a rifled gun and having that portion of its surface which normally contacts and is engraved by the rifling of the gun on firing formed in part by the periphery of an inset ring of essentially sintered polytetrafiuoroethylene which is conterminous with said surface and integral with the metal of said bullet.

2. An elongated lead bullet adapted to be fired from a rifled gun in which that portion of its surface which normally contacts and is engraved by the rifling of the gun on firing is in part the periphery of an inset ring of essentially sintered polytetrafiuoroethylene which is conterminous with said surface and integral with the lead of said bullet.

References Cited in the tile of this patent UNITED STATES PATENTS

Claims

1. AN ELONGATED BULLET OF LOW MELTING POINT METAL SELECTED FROM THE GROUP CONSISING OF LEAD AND LEAD ALLOYS, SAID BULLET BEING ADAPTED TO BE FIRED FROM A RIFLED GUN AND HAVING THAT PORTION OF ITS SURFACE WHICH NORMALLY CONTACTS AND IS ENGRAVED BY THE RIFFING OF THE GUN ON FIRING FORMED IN PART BY THE PERIPHERY OF AN INSET RING OF ESSENTIALLY SINTERED POLYTETRAFLIOROETHYLENE WHICH IS CONTERMINOUS WITH SAID SURFACE AND INTERGRAL WITH THE METAL OF SAID BULLET.