Now that I have my cans and multi cal SBR I am thinking about possibly a 9mm upper. What would be the best way to go with a manufactured upper ? Why not spend more cash I have a extra slot in my safe, My buddy has an Oly upper in 9mm but the mag release seems to be hanky to me with the sten mags. Can you go with the original mag release set up?
Does the mag block have to be pinned ?