Pass the Steel

In a war of automatic weapons such as this one, ordnance planners long ago foresaw that the armed forces might shoot their way right through the available supply of copper, the key metal in brass cartridge cases. They were right. By this week some 70 companies were making cartridge cases of steel in all sizes, .45-cal. to 105-mm.

Brass was ideal for cartridge and shell cases: it was easily worked, springy and slick and handled well in the gun. In World War I there was no necessity to mother a substitute. But World War II fire power is dizzily high; the U.S. produced more machine guns in one month of this year than in all of the last war. In February alone almost two million high-explosive shells were turned out, and almost one and a quarter billion cartridges. Brass could not keep up; one big cartridge plant (now changed over to steel) was slowed almost to a shutdown waiting for brass.

A lot of sweaty research has gone into adapting steel to cartridges for the hungry gullets of tommy guns, Brownings, Chicago pianos and automatic cannon. The researchers had plenty of troubles. One of the worst was the shortage of such alloying elements as nickel, chromium, tung sten and molybdenum. But eventually they developed a noncritical steel which would expand on firing to seal the breech, then contract quickly enough to permit ejection of the empty case.

It had to have other properties as well. Among the most important: the capacity to take the heavy punishment of deep drawing (i.e., being punched into hollow shape) without wrinkling, cracking, or breaking apart.

Drawing starts with a round chunk or disk of steel which is cupped, then elon gated by a series of punches and dies which work the metal into cylindrical shape. The open end is trimmed or tapered, the base machined to shape. Between draws, which harden the steel, the cartridge case must be annealed. To protect it from corrosion and sparking it must also be varnish-sprayed and baked.

Some of these operations are conventional. What makes steel cases metallurgically spectacular is the new (and still secret) application of known processes which permits extremely deep draws to close tolerances and gives steel the desirable properties of brass. All the hard way from the open hearth to the finished cartridge, U.S. industry has learned things about steel it never knew before.

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