It does not sound as if you are experienced in reloading for M1a’s. In my opinion the beginning of the process requires two critical tools: 1) A cartridge headspace gage, and 2) a small base die
This is a case gage:
This is how it works:
There is an assumption in this process, that the rifle is headspaced correctly.
Consumables in this process include the least sensitive primers you can buy. Currently there are only two “mil spec” primers on the market: CCI #34’s and the Tula7.62 primers. I would avoid all primers that claim to be “more sensitive”. Another consumable might be a primer pocket reamer. The cutting teeth wear on these things.
Steps
1. Full length size case with a small base die
2. Size case to cartridge headspace gage minimum.
3. Trim case
4. Ream primer pocket to depth
5. Seat primer below case head, inspect each and every primer to verify depth.
Slamfires occur because the primer was hit by a firing pin with sufficient energy to ignite the primer. This mechanism has a free floating firing pin. The probability of slamfires is never zero. If you look at George Frost’s book “Making Ammunition” you will see that even at the lowest, “No fire” primer test threshold, if 3 in ten million are allowed to fire, the lot is considered acceptable.
Steps 1, 2, 3 are simply there to ensure that if you have a slamfire, the bolt lugs are engaged. If the cartridge is too long, or too fat, bolt closure is delayed as the action swages the case into the chamber.
Step 4 and 5 reduces the possibility of a high primer.
Under no circumstances does anyone want an out of battery slamfire.
Small base sizing is best conducted with a good case lube such as RCBS water soluble or Imperial sizing wax. Spray on lubes will stick the case in the die.
Crimping is un necessary and will cause more problems than it solves.
Use powders in the IMR 4895 burn rate, such as AA2495/H4895 or IMR 4895. Don’t use powders faster than IMR 3031 or slower than IMR 4064.
I found AA2520, a ball powder, left a lot more residue in the gas system and I cannot prove that the better metering means anything on target. I don’t care for ball powders, stick powders are the best in this mechanism.
