Ive tried alot of the same things recently with some surplus 7.62x54r, which before my mosin nagant was getting 4 to 5 inch groups at 100 yards but trying all that other stuff I manage to tighten the groups to 3 inches. Something else I tried was I took 10 shells and measured the grain weight of the powder charge and took the average and evenly reloaded the 10 cases with the same charge weight backed off 1 grain from the average. Now I am getting about 1 inch groups. It was fun to do but personally a little to much work to get bench rest accuracy from ammo that was more then likely designed to be machine gun ammo. The ammo I used was 1960's Czech manufactured silver tip FMJ 148 grain LPS cartridges.