i also am going with the gas block bushing, not that i have a problem with ejection patterns(they consistantly throw 10 yds at my 3-4 o'clock) but want to tune my gun to the hilt!. as for the main spring if in doubt change it with a stock one or an extra power one you decide, stock is fine, but if you want to have your bolt to lock up with greater consistancy go with extra power. hope it helps. later