Since they chamber freely, shoot them at full size and you'll get best accuracy.
As a general rule, autoloaders will shoot best with the fattest bullet that will chamber freely, this because they can't tip as much on takeoff as a slimmer bullet. The exeption to this will be if the head space shoulder is too deep and causes lead to shave upon firing. The only solution for this problem is to open the forceing cone a little or seat bullets so the jamb into the rifling upon chambering so the bullet is already centered before firing. The second option is quite limited, and when limited it is because of the bullets design, not having enough bearing length, too much nose length or whatever, to allow smooth feeding.
