you won't get ANYWHERE using surplus/factory loads- UNLESS YOU WANT 3-4 MOA AT 100 m, or want minute of moose or something- start with the loads that are published under zediker or m14 match loads, or 308 match loads in the weight range you prefer- do that load, less a grain or 2 to begin with, and work your way up-it took me better than 4 YEARS of experimenting to find the "sweet spot" for all of my m14s and that was off a bench and firing every saturday and sunday- that's primers,powder, and bullets- the only constant was the cases were the same in every rifle- that's roughly a year per rifle, and FIVE ROUND GROUPS, too, people- THREE round groups tell you NOTHING
by starting out with the match loads, you get a sSTARTING POINT with half the work done for you by professionals- kind of like having someone else remove the overburden on a glory hole and you harvesting the hole itself