US3765297A

US3765297A - Non-eroding, lightweight cartridge cases

Info

Publication number: US3765297A
Application number: US00260076A
Authority: US
Inventors: L Skochko; R Donnard
Original assignee: US Department of Army
Current assignee: US Department of Army
Priority date: 1972-06-06
Filing date: 1972-06-06
Publication date: 1973-10-16
Anticipated expiration: 1990-10-16

Abstract

A lightweight cartridge case, preferably of aluminum, has a pliable and ductile sealing element disposed at a rearward portion of the case interior where a split in the case is expected to occur upon firing of the cartridge, the sealing element sealing off hot gas escape through the split, between the bolt and the weapon chamber, thus preventing surface erosion thereof and providing safety to the weapon operator.

Description

nited States Patent [191 Skochko et al.

[ 51 Oct. 16, 1973 1 NON-ERODING, LIGHTWEIGHT CARTRIDGE CASES [75] Inventors: Leonard W. Skochko, Philadelphia;

Reed E. Donnard, Huntingdon Valley, both of Pa.

[73] Assignee: The United States of America as represented by the Secretary of the Army, Washington, DC.

[22] Filed: June 6, 1972 [21] App]. No.: 260,076

2,936,709 5/1960 Seavey 102/44 2,935,945 5/1960 Brady.. 2,684,502 7/1954 Paulve [02/43 P Primary Examiner-Robert F. Stahl Attorney-Harry M. Saragovitz et al.

[5 7 ABSTRACT A lightweight cartridge case, preferably of aluminum, has a pliable and ductile sealing element disposed at a rearward portion of the case interior where a split in the case is expected to occur upon firing of the cartridge, the sealing element sealing off hot gas escape through the split, between the bolt and the weapon chamber, thus preventing surface erosion thereof and [56] References Cit d providing safety to the weapon operator.

UNITED STATES PATENTS 3,034,433 5/1962 Gronn 102/43 P 7 Claims, 8 Drawing Figures n4 x P 1 NON-ERODING, LIGHTWEIGHT CARTRIDGE CASES The invention described herein may be manufactured, used, and licensed by or for the Government for governmental purposes without the payment to us of any royalty thereon.

This invention relates to ammunition and more particularly concerns an improved cartridge case of lightweight material.

The development of aluminum cases for small caliber ammunition has demonstrated that success is contigent upon the solution of two problems. First, the case must provide a degree of strength, toughness, elasticity, etc., which will guarantee a typically satisfactory firing performance in the weapon for which the ammunition is intended. Second, in the rare event of a cartridge case failure during firing, the consequence of the failure must not be intolerably hazardous regarding damage to the weapon or injury to the operator.

Normally, solution to the first problem is approached by improving cartridge case material, mechanical design, and fabrication techniques. Significant progress has been made in this area and it appears now that with the new developments in materials, design and fabrication techniques, the functional reliability of aluminum cartridge cases can be made to approach acceptable levels. However, functional failures must be expected to occur occasionally with aluminum-cased cartridges, as they do with brass-cased cartridges, owing to rare defects in material, fabrication procedures or damage suffered by the ammunition in the field. Examples of the damage which may be inflicted upon ammunition in the field are scratching during delinking or linking operations, denting from negligent handling and corrosion pitting as a result of storage in unusual chemical environments.

Solution to the second problem, i.e., control of hazards to personnel and material in the rare event of a cartridge case failure has been approached by developing inherent safeguards in the ammunition, the weapon or both. Our invention is directed toward safeguards in ammunition and substantially overcomes the erosion problem which is inherent in aluminum-cased ammunition, and which must be solved before all such ammunition can be accepted as safe to weapon and firer in the field.

It is therefore an object of this invention to provide a lightweight cartridge case.

Another object of the invention is to provide such a cartridge case which will not erode as a result of the case splitting in the weapon during firing or due to other types of mechanical malfunctions, and which will not erode the adjoining weapon surfaces as hot gases and eroded case particles are blown through generated gas passages.

The exact nature of the invention as well as other objects and advantages thereof will be readily apparent from consideration of the following specification relating to the annexed drawings wherein like numerals represent like parts and wherein:

FIG. 1 illustrates a sectional view of a standard small arms cartridge.

FIG. 2 is a sectional view of a portion of a cartridge case embodying the principles of our invention at the instant of crack occurrence in a case wall.

FIG. 3 is a sectional view of our cartridge case taken along line 3-3 of FIG. 2.

FIG. 4 is a sectional view of the embodiment of FIG. 2, at an instant after crack occurrence.

FIGS. 5a 5d are sectional views of modifications of our invention.

Referring to the drawings, and more particularly to FIG. 1 thereof, a cartridge case 10 has on its outer surface a scratch 12, or an inclusion, fold or other flaw, such that they will cause a crack or split which will result in serious gas wash-out or erosion of the case and weapon. These cracks or splits may be caused by any one of several reasons including improper heat treatment of the case metal, internal imperfections consisting of voids, undissolved second phases, or brittle insoluble impurity components which could all be sites for crack initiation; external or surface imperfections such as scratches caused by manufacturing, handling, or weapon feed systems; stress corrosion cracking developed during storage; and failure of the case material because of lack of sufficient strength and fracture toughness.

The cartridge has the usual primer assembly 14, vent hole 16, propellant l8, and projectile 20. The weapon barrel is shown at 22 and clearance between the barrel and cartridge case is depicted generally at 24. Associated with the cartridge is the weapon bolt 26 and firing pin chamber 28.

Upon firing of the cartridge, the scratch 12, or the flaw, causes the case wall to split thereat before obturation occurs, thus permitting hot propellant gases to flow therethrough and into clearance area 24 and out between bolt 26 and barrel 22 causing erosion of case and weapon surfaces and severely threatening the safety of the weapon operator.

Our invention substantially overcomes this erosion and safety problem associated with case splits in lightweight ammunition by interiorly disposing a sealing element adjacent the area 12 wherein initiation of splits invariably occurs.

Very briefly, the sealing element, made of a pliable and ductile material, will be forced by the hot gases through the crack vertex and into the clearance area to effectively seal off the gas escape route. In order for our seal to function properly, two conditions must be present, i.e., (l) a pressure differential must exist across the seal to force it into the crack, as well as (2) total extrusion of the seal must not occur before the ballistic pressure cycle is completed.

To clarify the interplay of these conditions on our inventive cartridges and to more fully understand the invention, reference will now be made to FIGS. 2 and 3 of the drawings wherein a sealing element 30 is disposed within the cartridge as shown. The sealant may be any suitable deformable material, such as plastic, or elastomeric material such as silicone rubber, urethane, epoxy, polyethylene, and the like. Upon ignition of the propellant within the cartridge, a pressure P will be exerted against sealant 30 as indicated by the arrows. The sealant will move into crack 12 only if there is a force acting on it in that direction, that force being provided by the pressure differential developed between the interior, a portion of which is designated as X (propellant side), and the exterior, a portion of which is designated as Y (crack side), seal surfaces. The cartridge chamber pressure acts against the sealant interior surfaces whereas on the exterior surfaces of the sealant, and adjacent the case crack or split, acts the pressure corresponding to transient gas flow developed in the crack before the sealant has a chance to react. In the crack or split, a choked (sonic) flow corresponds to a static pressure of approximately one-half the chamber pressure. Thus, the effective pressure differential tending to force the sealing material into the crack will be approximately one-half the chamber pressure. To establish choking conditions adjacent the exterior seal surface near the crack 12, it is imperative for the sealant to be adjacent to interior case surfaces, thus preventing possible sealant movement away from the crack before choking occurs.

Since the internal cartridge pressure will be considerably higher than the yield strength of the sealing material, the sealant must be sufficiently ductile so as not to allow the propellant gases to cut a path therethrough. With sufficient quantity and proper selection of sealant material, complete extrusion will not occur before the ballistic cycle is over. Also, delay in extrusion is provided by the friction forces which try to prevent extrusion. Thus, by the time the sealing material 30 is totally extruded, the pressure inside the cartridge will have dropped to an insignificant level. This condition is illustrated in FIG. 4 where the extrusion column 40 is shown blocking egress of hot gases thru clearance 24 and out towards the bolt.

Modifications of our inventive cartridge are shown in FIGS. a through 5d; the sealants in FIGS. 50 and 5b being molded whereas potted sealants are illustrated in FIGS. 50 and 5d.

The molded

sealant configuration

42 and 44 of FIGS. 5a and 5b respectively are cylindrical and cup-shaped respectively. Each can readily be inserted into the cartridge case and suitably adhered or glued thereto or fastened through an interference fit before loading of the propellant.

The meniscus-shaped poured sealant configuration 46 of FIG. 5c may readily be formed by spinning the cartridge in a centrifuge, for example, until hardening of the sealant occurs. Of course, the faster the centrifuge is spun, the higher the sealant will rise up the interior of the case. To provide an opening between the primer and the propellant chamber or prevent entrance of sealant into the vent hole 16, a suitable object can be temporarily inserted into the vent hole and later removed after the sealant has hardened.

The sealant modification 48 of FIG. 5d may be centrifuge-spun and includes a brass or steel flash tube insert 50 secured or force fitted to primer assembly 14.

The insert provides a ready means for obviating the use of temporary objects in the vent hole and their subsequent removal when fabricating a seal of this type.

From the foregoing description, it is apparent that we have provided a lightweight cartridge case of improved design wherein a deformable plastic or the like is disposed in the case at a site where splits are anticipated during firing of the cartridge which will prevent hot propellant gases from escaping through the split to erode the case and gun surfaces and injuring the operator of the weapon.

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.

We claim:

1. In a cartridge having a case containing priming means disposed at a rearward portion and a propellant communicating with said priming means and forward thereof, a projectile forward said propellant, a weapon bolt and a weapon barrel cooperating with said cartridge, said barrel and said case forming a clearance area thereinbetween,

the combination therewith of the improvement comprising ductile or pliable sealing means within a lower portion only of said case and in contacting relation thereto, said sealing means extruding into said clearance area to prevent hot propellant gases from escaping rearwardly to cause erosion of the case and gun surfaces when a crack or split is formed upon firing of said cartridge.

2. The cartridge as described in claim 1 wherein said sealing means is a deformable material selected from the group consisting of silicone rubbers, urethanes, epoxies and polyethylenes.

3. The cartridge as described in claim 1 wherein said sealing means comprises a molded cylindrical configuration.

4. The cartridge as described in claim 1 wherein said sealing means comprises a molded cup-shaped configuration.

5. The cartridge as described in claim 1 wherein said sealing means comprises potted sealing means.

6. The cartridge as described in claim 1 wherein said case is made of aluminum.

7. The cartridge as described in claim 5 wherein a flash tube insert is disposed axially said sealing means. =l i

Claims

1. In a cartridge having a case containing priming means disposed at a rearward portion and a propellant communicating with said priming means and forward thereof, a projectile forward said propellant, a weapon bolt and a weapon barrel cooperating with said cartridge, said barrel and said case forming a clearance area thereinbetween, the combination therewith of the improvement comprising ductile or pliable sealing means within a lower portion only of said case and in contacting relation thereto, said sealing means extruding into said clearance area to prevent hot propellant gases from escaping rearwardly to cause erosion of the case and gun surfaces when a crack or split is formed upon firing of said cartridge.

6. The cartridge as described in claim 1 wherein said case is made of aluminum.

7. The cartridge as described in claim 5 wherein a flash tube insert is disposed axially said sealing means.