My main carry gun is a 4516-1. Got it LNIB with two mags that have yellow followers and are marked to be used only in the 4516-1. I have tried to find out the reason for this and have never got a real or full answer. I have orange & black follower mags and all work great in the gun. Have never had any troubles. If you go with a 4516-1 you will be pleased.