RE: rem 7400?
Ive had my hands on dozens of the various jam masters, and these rifles require more attention than your average hunter is willing to devote to keeping a rifle shooting. Mainly they require cleaning after shooting. Something most deer hunters dont know anything about. They have put alot of money in the pockets of mom and pop gunshops though. I doubt if it will matter what ammo you try first. Just try several and pick the best. One thing about gas operated guns is that you need to be careful not to zero it hot. Its a pain to wait, but they will shoot erratically when hot. Let it cool between shots and go back and check zero when the gun is completely cooled. Good luck.