I have a pair of these mags, running a bighorn origin with a mpa chassis. Both ran with no failures right out of the package. Only thing is to make sure rds are loaded level, they will let the rounds sit in a nose down position if slid forward as far as possible. Just ensure that they are pushed all the way to the rear and they sit flush. The old army tap of the magazine on your helmet(not that I am wearing a helmet while shooting anymore) works well.