This article is an excerpt from the Gun Digest Book of Classic Combat Rifles.
Reports from Vietnam of failures to extract in the field caused the subcommittee great concern. They investigated, finding the major contributor to malfunctions was ammunition assembled using Ball powder. The change from IMR extruded powder to Ball powder in 1964 for the 5.56mm ammunition was neither justified nor supported by test data, they found. The subcommittee also found the Ball propellant sole-source position enjoyed by Olin Mathieson for many years — and their close relationship with the Army — may have influenced Army Materiel Command.
They felt the AR-15/M16 rifle, as initially developed, was an excellent and reliable weapon. Further, certain modifications made to the rifle at the insistence of the Army — also unsupported by test data — were unnecessary. For example, both the Air Force and the Marine Corps found no evidence to support the expense and possible problems of the manual bolt closure (forward assist) device.
Gene Stoner was called to testify at the congressional hearings to explain the extraction problem; he explained the failure to extract was due to the use of Ball powder.
Gene Stoner [To Mr. Bray]: “Well, the cartridge tends to stick under high residual pressure in the barrel, and of course with this too-soon action you also have a higher bolt velocity. In other words, your bolt is trying to open at higher speeds, so you have an aggravated condition where the cartridge is tending to stick in there a little longer or a little harder, and you are also giving it a harder jerk by driving the bolt faster.”
Mr. Bray [To Gene Stoner]: “Then a faster rate of fire could cause that situation (failure to extract)?”
Gene Stoner [To Mr. Bray]: “This is probably one of the worst conditions you can get, by increasing the cyclic rate.”
Basically, Ball propellant causes the bolt to open prematurely, before the spent cartridge case has had sufficient time to contract. The result is the extractor shears off the rim of the spent cartridge case — which sticks in the chamber. Ball and IMR powders create the same peak pressure but the Ball powder reaches its peak much faster than IMR powder, causing a significant increase in the cyclic rate of fire.
Ball powder leaves significantly more fouling in the chamber and bolt assembly. Gene Stoner also pointed out the rifle had gone through more than 22 changes from his original design and neither Colt nor the Department of Defense consulted him on how some changes would impact his design.
The forward assist was one of the changes on which he was not consulted and Mr. Ichord asked Gene Stoner his opinion of the device.
Gene Stoner [To Mr. Ichord]: “I wasn’t in on that, except I was told the Army insisted on it. There were reasons for it.
One reason was that they felt that due to the fact that the M1, and the M14 rifle, and the carbine had always had something for a soldier to push on; that maybe this would be a comforting feeling to him, or something. I could never quite get it through my mind that it was necessary. I did not really advise it. I thought it was a mistake, myself. But I made my thought known to the people.”