Stoner intended the AR-15 to use ammunition loaded with stick (IMR) powder. You may remember that there was difficulty in loading 5.56 M193 with IMR to the velocity required to penetrate a steel pot at 500 yards and maintain chamber pressure.
Then in 1968 the use of stick powder was suspended in the loading of M193.
So been thinking I was going to have to use hand loads in my Model 01, 02, and XM16E1 clones, or just live with Ball powder induced excessive bolt velocity and the battering that goes with it.
Well, looks as though the Serbs are to the rescue:
Reading the test results I see that the Serb ammo achieves proper velocity, lower port pressure, and we hope safe chamber pressure at the same time. So there you go, early 60's spec M193.
For those that don't know, the early 1960's AR-15 did not have a functional buffer, but instead used a lightweight recoil spring guide called an edgewater. If you don't have a light weight recoil spring guide then you may well have some issues using this ammo (as did the tester).
Ya learn something new every day! I knew Stick (Stickman) became a ARFCOM dealer, but had no idea he had his own powder!
IMR is a extruded powder or "stick powder". IMR4475 is what Remington loaded for ArmaLite for use in the AR-15. The original Colt/ArmaLite AR-15 used a edgewater recoil spring guide. This spring guide is significantly lighter then the buffer used from December 1966 on.
THE BLACK RIFLE page 136
November 1963 Colt wins an award for 104,000 M16 and XM16E1 rifles.
Army seeks ammunition to go with rifle awards
THE BLACK RIFLE page 141
Prior to acceptance individual rifles are tested to insure they meet cyclic rate specifications.
Tolerance limits for cyclic rate are set at 650-850 rpm.
March 24-25 1964 Colt reports that six out of ten exceed 850 rpm's with WC846, a Ball powder. One out of ten exceed 850 rpm with IMR4474.
In April 1964 the Air Force grants a waiver to extend rpm specs to 900 rpm for their M16 rifles. The Army grants Colt a monthly waiver extending the rpm limit to 900 rpm through out the Summer of 1964.
Ammunition loaded with CR8136 (extruded) is delivered to Colt for the sole purpose of acceptance testing and is delivered in August of 1964.
Army suspends the 900 rpm waiver because CR8136 meets cyclic rate specs.
December 1964 Remington drops CR8136. As with the prior extruded powder IMR4475 chamber pressure limits could not be met. Remington now loads with Ball powder, specifically WC846. WC846 Ball powder is now used by all three M193 manufacturers.
Colt runs out of CR8136 in the Spring of 1965.
September 1965 test results:
EX8208 (later named 8208M) extruded powder 854 rpm (used in production starting in June 1966)
WC846 Ball powder 880 rpm
THE BLACK RIFLE page 198
November 1965 Testing shows ball powder increases cyclic rate 92-135 rpm over extruded powder.
THE BLACK RIFLE page 199
THE BLACK RIFLE page 200
THE BLACK RIFLE page 203
THE BLACK RIFLE page 203
THE BLACK RIFLE page 211
THE BLACK RIFLE page 212
THE BLACK RIFLE page 269 shows M16A1 test results with the newer heavy buffer.
WC846 815 rpm
IMR 8208M 650 rpm
THE BLACK RIFLE page 274
AMERICAN RIFLEMAN April. 1968 page 42
AMERICAN RIFLEMAN Feb. 1978 page 38
Wow . . . .
Great compilation Ekie! Thanks!