RELOADING FOR THE M1 GARAND / M1A RIFLE
Several bullets work very well in the M1. For plinking and practice, the inexpensive 147-150 grain FMJ bullets work great with the IMI 150 grain FMJBT. For match shooting, the high quality (and price!) 150-180 grain HPBT match bullets can't be beat. The 155 grain Sierra Palma and the 168 grain Match King are considered best, but any name brand match bullet will shoot great. The 180 grain and heavier bullets are usually used only at 600 yards or longer ranges and have no advantage on the shorter courses.
The M1/M1A, while a very strong design, is powder sensitive. Gas port pressure, not chamber pressure, is the critical factor. You must use powder with a burn rate between and including IMR3031 and IMR4320. Slow burning powders increase gas port pressure which over stresses the operating rod bending or breaking it. Best performing powders are usually IMR4895, IMR4064, AA2520.
Any large rifle primer works fine. There are only two main considerations. First is primer hardness. The M1/M1A has no firing pin return spring and can be susceptible to slam fires so hard primers can reduce the risk of the occurrence. CCI and Winchester are considered "hard" while Federal are "soft". CCI now makes a Mil. Spec. primer which should be great for semi-auto's like the M1/M1A. The second consideration is standard or benchrest primers. For reduced courses of 200 yards or less standard primers are fine, but for 300 yards or longer, Benchrest primers are a must. There is a measurable difference in consistency between the two.
G.I. cases will last the longest in your rifle. But even G.I. match cases are below commercial cases in overall quality. They vary in internal dimensions by a wide margin. As far as commercial cases, Remington and Federal are excellent. Winchester is good but doesn't seem to hold up as long.
PREVENTING SLAM FIRES:
Several things can be done to help prevent this from occuring. First, I recommend using the RCBS Precision MIC to gauge the fired case * headspace of your rifle. By using this tool to help setup your resizing dies , it is easy to obtain an average resized case headspace of .003" below the fired case average of your rifle. What this does is help to provide enough clearance between the bolt face and the cartidge head so the full impact of the bolts inertia at closing is not being absorbed by the live round in the chamber. Another good check is to take a resized case and slip it into your chamber. Attempt to close the stripped bolt on the case. There should be very little or no resistance as the bolt goes closed. Perhaps the most important thing in preventing slam fires is proper primer pocket cleaning and primer seating. First be sure to clean your primer pockets prior to seating the new primers. I would also strongly recommend using a primer pocket uniforming tool ** to true and cut the pockets to between .128" - .130" in depth. This allows for full primer seating to occur at just below level with the case head which helps to insure that you get no high primers. Be sure that you don't get too forecful when seating your primers and crush them into place. This can give an oversensitive primer. By following the above few extra steps you can greatly reduce the chance of a slam fire ever occuring. This type of incident should not be taken lightly. It is a very dangerous condition. If you rifle slam fires regularly, please have it checked, along with some of your ammo, by a qualified gunsmith who is knowledgeable about service rifles.
* Be sure to disable the gas system and fire the rounds single shot when obtaining the cases used for measurement. This gives a much more consistent, accurate reading. Plus, use ammo that gives an initial reading of zero or slightly under that on the Precision Mic. This should allow for full case expansion to match your chamber.
** A primer pocket uniforming tool that has an adjustable carbide cutter is available from Midway (800-243-3220). This tool is nice in that it can be used in the chuck of a hand drill or drill press which speeds up the process nicely. Plus, it has cutters for both small and large primer pockets.