Tankmech; Here's some backround on the M1 you might find interesting.
From the article "Accurizing The M1 Rifle, by J. B. Roberts, Jr. "When the glass bedding job on my DCM M-1 was completed, the rifle, which had sprayed hits all over the SR bullseye, shot well within acceptable criteria for the National Match M1 rifle. Those limits were not tough; 3 1/2" average extreme spread for three shot groups at 100 yards range; no single group over 5" extreme spread."
Chances are that your target hits are close to the above 1961 standards. If you can get 4" groups @ 100yards, that's pretty good shooting, for a M1 Garand.
Enjoy your M1, and have fun!