the A1, as issued to Marine snipers, were more accurate over the A4s. Any reason for this?
Might have something to do with the fact that the USMC 1941 sniper had a 8X Unertl instead of a 3X Weaver scope. About three times the scope, if you go by the price at the time.
I think the OP's rifle is a common sporterized '03A3. I cannot see the A4's offset markings and the bolt handle looks gunsmith bent instead of arsenal ground out.