Ammunition Development

light armor at Aberdeen Proving Ground, a series of computations were made to determine as nearly as possible the expected performance of various calibres within the limits of calibre .50 to calibre .80. It was found that a calibre .60 cartridge with the following basic characteristics, was the lightest that could be expected to meet the penetration requirements:

Calibre 0.60 inch

Weight of Bullet 1,200 grains

Muzzle Velocity 3,420 feet per second

Remaining Velocity at

500 Yards 2,850 feet per second

The requirement was formally established by the Ordnance Committee on 7 February 1939.

Frankford Arsenal and Aberdeen Proving Ground were requested to make a study of a complete round with these characteristics and to furnish a suggested design. A contract was negotiated with the Winchester Repeating Arms Company, to develop a calibre .60 complete round, which would satisfy the requirements and to manufacture Mann-type barrels for testing the rounds.

The performance of the Winchester ammunition was unsatisfactory. Erratic flight of the bullet resulted in failure to penetrate armor plate to 1.25 inches at 100 yards. Examination of recovered bullets revealed uneven engraving of rifling. The bullet was so unstable, that in the majority of cases it was not accurate at ranges as short as 50 feet. On completion of the Winchester Repeating Arms Company contract in September 1940, the project was transferred to the Frankford Arsenal Ordnance Laboratory.

On 22 May 1941, the Ordnance Committee approved the development of a calibre .60 aircraft machine gun. In October 1942, the Army Air Forces reiterated interest in the development of the aircraft machine gun and requested three test models. On 27 October 1942, a conference wras held at Frankfort Arsenal to initiate the development and manufacture of armor-piercing and tracer ammunition for the calibrc .60 anti-tank rifle and aircraft machine gun.

On 22 May 1943, the requirement for the calibre .60 anti-tank rifle was terminated bv the Ordnance Committee because ot the relative ineffectiveness of such ammunition against the newr types of heavily armored enemy vehicles. Development of calibre .60 ammunition for the aircraft machine gun continued. By 2 December 1943, ball, armor-piercing, incendiary, and armor-piercing-tracer ammunition had been developed.

In the initial development of calibre .60 ammunition, primary consideration was given to the armor-piercing cartridge. A duplicate round, with a mild steel core in place of a hardened steel core, was considered for training purposes. In the course of development work on the armor-piercing bullet, it seemed advisable to develop base-capped bullets with the bare steel cores. Mild steel cores were used for tests to determine bullet stability.

As originally conceived, the calibrc .60 cartridge case represented, with minor dimensional differences, an expansion of the calibre .276 cartridge case developed during the period 1925-1929.

The imminent production of ammunition on a relatively large scale in December 1943, as well as attempts to increase barrel life by increasing the depth of rifling, led to the development and testing of a number of modifications of the original cartridge case. The modifications arc listed in the following table, together with the designations assigned to them.

Model of Case

Description

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