Hey folks. Long story short, I managed to use the wrong load data for a ton of Garand ammo. What I now have is a few hundred rounds loaded with 44.2gr of IMR4064 behind a 168gr Hornady A-max. Do you guys think I'll have any issues with the gas system short stroking? Thank you all in advance.
Garand loads: How bad did I botch this...
- Thread starter RNeils125
- Start date
Welcome to the forum.
No. 47-48 grains of that powder would likely have served you better from an accuracy standpoint and how cleanly the powder burns, but being 10% below that is not going to cause gas system problems in a normal Garand with a normal strength recoil spring and piston and cylinder diameters within spec. It is true that pressure in the barrel will be about 10% lower near the muzzle, but the bullet will also be going more slowly, so the time between when the bullet base passes over the gas port, exposing the port to pressure, and the time the bullet clears the muzzle and pressure drops, will be longer. Thus the gas impulse, which is the pressure multiplied by exposure time, will not be very different. And it is the impulse that determines how much gas is driven into the cylinder.
Below is a graph of calculated impulse with IMR4895 with 152 and 168 grain bullets. You can see it goes all the way down to 39 grains with a 168 grain bullet and how little the impulse changes as a result. You can also see that it peaks at about 46 grains and beyond that it actually drops slightly. This is due to the higher peak pressure of the heavier loads giving the bullet acceleration disproportionately higher than the growth in muzzle pressure with the charge weight increase. For this reason, the common belief that maximum loads of 4895 or 4064 (both within the Garand-acceptable burn rate range) will damage the gas system are flat wrong. This has been measured to be a true phenomenon by Ericc at Garandgear.com. The only damage from full loads are in beating up the stock bedding more and also not always being the most accurate loads.
No. 47-48 grains of that powder would likely have served you better from an accuracy standpoint and how cleanly the powder burns, but being 10% below that is not going to cause gas system problems in a normal Garand with a normal strength recoil spring and piston and cylinder diameters within spec. It is true that pressure in the barrel will be about 10% lower near the muzzle, but the bullet will also be going more slowly, so the time between when the bullet base passes over the gas port, exposing the port to pressure, and the time the bullet clears the muzzle and pressure drops, will be longer. Thus the gas impulse, which is the pressure multiplied by exposure time, will not be very different. And it is the impulse that determines how much gas is driven into the cylinder.
Below is a graph of calculated impulse with IMR4895 with 152 and 168 grain bullets. You can see it goes all the way down to 39 grains with a 168 grain bullet and how little the impulse changes as a result. You can also see that it peaks at about 46 grains and beyond that it actually drops slightly. This is due to the higher peak pressure of the heavier loads giving the bullet acceleration disproportionately higher than the growth in muzzle pressure with the charge weight increase. For this reason, the common belief that maximum loads of 4895 or 4064 (both within the Garand-acceptable burn rate range) will damage the gas system are flat wrong. This has been measured to be a true phenomenon by Ericc at Garandgear.com. The only damage from full loads are in beating up the stock bedding more and also not always being the most accurate loads.
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