US2193664A - Ammunition - Google Patents

Description

Patented Mar. 12, 1940 AMMUNITION No Drawing. Application September 3, 1936, Serial No. 99,310

2 Claims.

This invention relates to the manufacture of shot, and contemplates shot made by a metal hitherto unused for this purpose as well as a method for the production of shot from this 5' metal.

Commercial shot as used in shot gun shells or cartridges consist chiefly of lead, hardening agents such as antimony and/or arsenic being present in small but controlled amounts. Such shot are manufactured by preparing a melt of the lead,

running the molten metal into a sieve or dropping pan, upon the underside of which droplets of molten lead are formed to a size determined by the size of the apertures in the pan and the temperature and composition of the metal, and,

upon reaching the size so determined, are detached from the pan by their own weight and fall through the air a distance of the order of 130 feet. During theirfall, they are solidified sufiiciently to withstand impact with a cushioning body of water placed at the bottom of the dropping tower, from which they are removed as fully formed shot substantially ready for use. The number of spherical shot pellets required in the ammunition industry is such as to substantially preclude manufacture by the conventional metal working methods of casting, grinding or rolling.

Lead shot are subject to certain disadvantages. They are poisonous to game birds, when taken internally; the poisoning of ducks in the marshes over which there has been a great dealof shooting having become a problem of such magnitude as to receive the attention of the United States Biological Survey. Moreover, the density of lead 85 is so great that for some uses lead shot are undesirably heavy. With a given amount of energy lighter pellets may be given a substantially higher initial velocity, which velocityis sufficiently sustained to accomplish the desired purpose. Air

rifle shot, for example, should be projected with considerable velocity, but an excess of residual energy after a flight of medium range is undesirable. The need for non-poisonous and lighter shot has long been recognized, but prior to the present invention, it has been deemed impracticable to drop shot of the lighter, harder, nonpoisonous metals. Lead offers a unique combination of low melting point and low heat of fusion, which permits the dropping of lead shot in the manner heretofore described. The melting points of other metals are usually so high that it is impracticable to secure a melt of sufficient fluidity to be dropped through apertures of small size, their surface tension characteristics are 5 not such as to form spherical shot on dropping,

or their heat of fusion and/or heat generated by surface oxidation is so great that they do not solidify upon dropping any practicable distance.

The present invention comprises the discovery that by proper treatment and control shot may 5 be dropped which consists almost entirely of zinc. Pure zinc has a melting point of about 788 F., and becomes sufiiciently fluid to run through a dropping pan at a temperature of about 1150 F. At this high temperature, however, it is diffi- 10 cult to prevent rapid oxidation of the melt in the kettle, the metal tends to stream through the apertures in the dropping pan instead of forming spherical globules, and such separate particles as are formed do not always solidify upon dropping down the tower. While it is possible to drop shot of substantially pure zinc, they are accompanied by an amount of scrap metal which tends to be excessive.

The process and the yield are both greatly improved by the addition to the zinc of a suitable amount of an alloying substance such as sodium or a commercial sodium-zinc alloy. The metal then resists oxidation, both in the melting kettle and dropping pan and while falling down the tower. It likewise acquires such a surface tension as to form spherical pellets and becomes fluid at much lower temperatures. The droplets, due to the improved surface tension, resistance to oxidation, and lower temperature at which they leave the pan, are solidified in the air drop of about feet, instead of remaining in such a liquid or plastic state that they are broken up upon impact with the water.

The sodium content may vary from about .1 of 1% up to or even substantially beyond a content corresponding to the composition of the Known zinc-sodium compound of the probable formula NaZmz. This is about 2%. If sodium in excess of the compound composition quantity is present, the excess, being free, as distinguished from being in combination with the zinc, reacts with water, and in water the shot disintegrate. For some purposes this characteristic is advantageous. The loss of water fowl by lead poisoning comes about through the swallowing by the water fowl of poisonous lead shot which have accumulated as a result of extensive shooting over the shallow water feeding grounds. By using an eX- cess of sodium in zinc shot, the shot, although non-poisonous, are made to actually disintegrate so that no accumulation of shot is possible. If the characteristic of disintegrating in water is not desired, as for shooting at flying targets or for air rifle shot, the sodium content should be below the compound composition quantity. Generally stated, increasing the sodium content lowers the dropping temperature. A low dropping temperature is desirable, particularly in a standard dropping tower of a height of about 130 feet, since from the lower temperature there is less heat to be lost before the shot droplets solidify. However, other factors such as specific heat and heat of fusion have a very important bearing on solidification and sphericity. If the metal is readily susceptible to oxidation, the heat generated at the surface of the droplets while falling down the tower may substantially exceed the heat of fusion. Likewise, surface oxidation of the droplet before it is detached from the dropping pan may prevent the formation of spheres, causing the droplets to assume an elongated instead of a spherical shape. It is believed that the sodium or oxides of sodium not only act as flux, but likewise prevents surface oxidation of the Zinc and supplies such a surface tension as to materially assist in the forming of spherical, rather than elongated, droplets. l sodium content of the order of is preferred. Shot according to this invention have been dropped successfully with temperatures as high as 1100 F. and as low as 810 F.

It has been found that for a given size of shot the dropping pan apertures for zinc or a zincsodium alloy should be somewhat smaller than for the same size of lead shot. "Under some circumstances it is desirable that during dropping the dropping pan be subjected to a series of rapid light blows. This tends to prevent clogging of the apertures but likewise tends to increase the of the droplets formed beneath the apertures of a given size. Cooling and solidification in th tower may be facilitated by providing an upward draft of air of greater or less intensity or by introducing into the tower a fine spray of water. Similar results can be secured by increasing the height of the tower. It appears to be essential that the droplets be in a substantially solid condition before impact with the water, the water acting chiefly as a cushioning medium to prevent distortion of the shot by direct impact with a solid surface.

The shot thus made may be plated if desired with one or more metals. For example, a plating of copper applied directly or a plating of nickel upon the shot and a surfacing of copper on the nickel. Such plating may be accomplished by any of the known plating methods, including contact plating by dropping the shot through the tower into a plating solution, rather than into water.

Zinc or zinc-sodium shot as heretofore described are used in the same manner as other shot, either for individual iring in air guns or for loading into shot shells for general or particular uses.

As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that I do not limit myself to the specific embodiments thereof except as defined in the appended claims.

l/Vhat is claimed is:

"he process of making substantially spherical shot 5 'table for use in the manufacture of triciges, which comprises alloying than 2% of sodium, separating the molten alloy into globules at the top of a shot tower, and dropping the globules a distance sufficient to enable them to solidify into substantially spherical shot.

2. In the manufacture of substantially spherical shot suitable for use in shotgun cartridges and consisting substantially of zinc, the method of controlling the fo ation of spherical pellets and preventing excessive oxidation while droppin such pellets through a distance sufiicient to substantially solidify them, which comprises a1- loying with the zinc not more than 2% of sodium, separating the alloy into globules at the top of a shot tower, and dropping said globules through said tower into an impact cushioning medium.

JOHN R. EALDER. THOM -S BAILEY CURRAN.