Quote:
The pressure curve of M1 gas system safe ammo is determined by bullet weight and burn rate of the powder used, NOT by muzzle velocity.
Trying to figure out by rated velocity whether or not a load is M1 safe is not possible. It is quite easy to create two different loads, both using the same bullet, but with two different powders and have the one with the LOWER velocity have a HIGHER gas port pressure.
|
Yes and no. Lot acceptance of Garand powder had a velocity criteria, a breech pressure criteria, peening, and a gas port pressure criteria. I have the lot acceptance sheets for two different lots of WC 852. At the powder vendor they measured pressure in a pressure barrel, and velocity. There is the notation that a couple of Garands functioned with the ammunition, and there is the comment that no peening was observed.
Velocity was controlled. I can guess because they had all these rifles with permanent marking on the elevation knob, maybe there were other reasons. But ammunition was kept within velocity tolerances. They also “corrected” the contractor pressure barrel reading to the Frankford Arsenal pressure barrel. They fired a round that met the 2740 fps/pressure criteria in the Frankford Arsenal pressure barrel, and took the reading in the contractor pressure barrel. And used the differences as a “correction”.
What I saw was that the Frankford barrel was a fast barrel, and velocities in the contractor barrel were closer to 2650 than 2740.
The first year the CMP contracted Federal Ammunition to use in the Garand Matches, the ammunition was too hot. Now it may have been made to SAAMI specs, but the stuff chronographed close to 2900 fps and it caused malfunctions. My shooter had his gun jam up because the port pressure was too high. This happened to a lot of people. It took about two years for the CMP to change the spec, but now CMP ammunition shoots around 2700 fps.
So I will say the first statement is mostly correct, particularly when you get to the safety aspect.
As for velocities, without pressure gages and port pressure gages, how can we determine if the ammunition is right for a Garand?
Velocities are the easiest way to determine if you are loading correctly for a Garand. That is use powders that give appropriate port pressures (4895, H4895, 2495, AA2520, etc) and load them up to the velocity you get when you fire LC in your rifle. Which will be between 2650 – 2700 fps with a 150 grain bullet.
Your Garand was designed to use ammunition made in 1936. It was not hot ammunition, even by the period, and it is certainly not hot today. Many lots of ammunition were in the 40,000 psi range.
When you use modern ammunition at high port pressures you will have malfunctions. The rifle will be opening and closing too quickly. You may have all sorts of strange clip jumping, bolt overrides, failure to feed, failure to extract, who knows. And it will beat up the rifle as things are slamming and banging too much.
I reload for my Garands, a nice reload that I have used is 150 gr SMK, 47.0 grs IMR 4895 LC cases CCI #34. The same load with a 168 SMK will function just fine in a Garand.