I was just out to the range with my Garand yesterday. As mentioned above, I have found my best loads are built on IMR 4895 and 4064. Yesterday my 150 gr FMJBT over 48 gr of IMR 4064, the starting load in the Lyman 49th, produced the best groups. One other thing to keep in mind when loading for the Garand, or any other gas gun, is the fact that they employ a floating firing pin that will lightly strike the primer when chambering a round. The combination of a floating firing pin and a fragile primer, or one that is not seated properly, can cause a "slam fire" where the round will be fired before the breech is locked. This can be dangerous as well as startling. (Don't ask me how I know this.) I use CCI #34 mil-spec primers for my Garand and #41 in my AR clone. I also use a hand primer to assure that the primers are seated properly.
Good luck and enjoy shooting a great gun.
Frank