Purchase a Wilson Type Cartridge Headspace gage. I like the simplicity of a “go” , “no-go” gage.
Good pictures and description at
http://www.realguns.com/Commentary/comar46.htm
Full length resize the case to gage minimum. I recommend using small base sizing dies. Always use small base dies if using firing range pickups, or if you are shooting this ammunition in a commercial chamber. Such as a match Garand.
Trim cases below max trim length. I trim to minimum.
Prime cases by hand, verify that each primer is below the case head. It is not a bad idea to ream pockets to depth. Do not use Federal primers, Federals are the most slamfiring primer ever in Garands: they are too sensitive for gas guns. I recommend CCI #34 primers or Tula 762 primers as they are advertised as being Mil Spec.
Use IMR 4895 or equivalent. H4895 and AA2495 are virtual duplicates, the main differences due to lot differences. A bud of mine uses 46.0 grains IMR 4064 with his 168’s, IMR 4064 does not throw as well as 4895 but he weighs all his charges. You should use no powders faster than IMR 3031 or slower than IMR 4064. Good rule of thumb.
For 150 grain bullets keep your velocities below 2700 fps, better to average 2600-2650 fps which is equivalent to GI ball ammunition in my rack grade rifles. Match ammunition was loaded with 174's and that is the heaviest bullet to use in a Garand. That load chronographed at 2640 fps in military acceptance barrels. No one should try to push a 174/175 any faster in these mechanisms. The gas system was not designed for magnum level velocities. As long as you stay within military velocities with the proper powders you don't need to use a vented gas cylinder lock plug.
I shot Hornday 150 FMJ's, they are not target bullets, but they shot a lot better than military bullets.
Sierra 175 Matchkings are wonderful bullets and I use them at 600 yards.
30-06 cartridge OAL should not exceed 3.30” for best clearance in the magazine. Shorter is fine.
My load with 168’s is very accurate. This is the load I use out to 300 yards.
