On the RIA 10, the problem is on the slide lock. It doesn't go deep enough into the magazine to allow the follower to catch and hold open the slide. Pulled the slide lock from my kimber, and inserted it, into the RIA, and it functioned perfectly on all my mags. Seems the catch on the RIA slide release is 2/1000ths shorter than the kimber. I'm thinking of contacting RIA, and see if they will send me another slide release lever.