The main trick with the Garand is not to use powder that is slow. Slow powders create higher muzzle pressures, and that can bend the operating rod.
The Hornady manual has a separate section for Garand loads, but a lot of us have recipes. I would say that IMR 4064 has a well-deserved reputation for producing accuracy with this rifle. It is a little bulkier than some, but works well. You can use something as fast as IMR 3031 with if for 150 grain bullets. For the 168 and 175 grain match bullets it will do better with either IMR 4895 or H4895 or the IMR 4064 I already mentioned. Some are using Varget, but see my note below.
CCI makes a special large rifle primer for these guns and the M14 style guns called the #34. It is harder than commercial primers. I've not had a problem with standard commercial primers, but board member Slamfire sure has. If you can find some, it's probably worth the extra safety margin.
Commercial brass is not as tough as Lake City military brass, and the semi-auto can yank hard on brass and bend rims. For that reason, it's a good idea, if you are not firing in a match that prohibits it, to get one of the
adjustable vented gas cylinder plugs. These allow extra pressure to be bled out of the gas cylinder, sparing the op-rod (op-rods are in short supply), and it can be tweaked until the brass falls right near the shooter instead of somewhere in the next county. That means it is being easier on the brass.
I've had good luck in the past with Remington brass having similar capacity to Lake City, but haven't had occasion to buy current stock.
Some will advise you to get a small base die. You may need it if you are sizing brass fired in another gun for the first time. Usually, once you have fired a case in your gun, the chamber fit will allow a standard die to resize it adequately. I would, however, measure the new brass diameters at the shoulder and about a quarter inch forward of the head and also the head to shoulder headspace length with a tool like the RCBS precision mic or the Hornady or Sinclair case comparators that adapt your calipers to the task. Make sure all these dimensions go back at least 0.002" after you've finished sizing.
If you buy from the CMP the gun will have been inspected to ensure it is within gauge tolerances. That's a good choice and will reduce the chance of a slamfire occurring.
For 150 grain bullets, I find the Hornady FMJ's to be the most economical ones that produce decent accuracy. For the full 600 yard course, I use the Sierra 175 grain MatchKing. You can use it to mimic the last M72 load when assembled using a CCI #34 primer and 46.5 grains of IMR 4895, though I use 46.6 grains of IMR 4064 instead because it gives better case fill and lower port pressure, and seated to 3.267" in either Remington or Lake City cases.
