It is generally recommended to load between 147-173gr bullets for the M1 Garand or M14 using standard jacketed bullet loads.
A powder in the suitable burn rate range for the action of this type of semi auto gas rifle such as IMR 4895, H4895, AA 2495, BL C2, H335, Win 748, IMR 4064 (and there are others).
Full Length size all brass every loading and trim when needed. Make sure primers are seated flush. CCI and Win are good primers to use for these rifles.
I use the manuals starting load data and work up the same as any for the powders/bullets noted above.