Addendum to prior posting. After being sent another unit from targetmaster and trying every kind of ammo I could find, I finally gave up and sent both units back. Shortly after, I received a check for my purchase price together with a very nice personal letter apologizing for my inconvenience. The conversion just would not work in "My" Bushmaster carbine. I think the hammer spring was (is) too strong, since the unit would not fully eject the empty most of the time and when failing, would not cock the hammer. To make a long story not much longer, the unit is well made and the people running targetmaster could not be any nicer.