Re: need help w/ M1A
Standard load for many a year; A Lake City Match case, with about 41.0-42.0 grains of 4895 under a 168, and go to the range. If the gun doesn't shoot this load, you've got a gun problem. Back when the M14s ruled the roost, that's the load that 98% of the shooters on the line would be using.
There's other options, of course. Reloder 15 is the powder that current lots of M118LR ammunition is loaded with. This uses a 175 SMK, but the powder's equally at home with a 168. Ditto for Varget and 4064, they'll all work just fine.
Couple of things to go with the proper care and feeding of an M1 or M14;
1) full length sizing ONLY! Ignore any and all advice to the contrary, it'll get you in trouble, fast. Forget about bumping the shoulder back .001" like you would a bolt gun. Go .003" at a minimum, and probably .005-.006" at the maximum.
2) Avoid using bullets heaver than 175 grains, or any powders that are slower burning than those in the same neighborhood of 4895, 4064, Varget or RL-15. This is what the gas systems on these guns were designed to work with, and deviating from them will do bad things to the gas system, and ultimately, the gun itself.
3) Make sure your primers are seated properly, and well below the case head. remember that the M1/M14 family uses a floating firing pin, and will strike the primer lightly when the bolt is closed. Chamber a round sometime and then exrtact it, and you'll see the firing pin dimple on the primer. For this same reason, avoid using "soft" cupped primers. Slam fires aren't good, and will ruin your day.
4) DO NOT get carried away with case prep. Neck turning and all that good stuff is not only a waste of time on a Service Rifle, it's potentially dangerous. Besides, the brass is goiing to last three (3) firings, maximum, and needs to be tossed after that third firing. Remember, it ain't a bolt gun, and the rules are different here.
5) and about the M16/AR-15 . . ..