<><> Gargoyle, I had the same thing happen on my UC ss. It was the magazines I was using, CMC. It seems when the last round was fed, the follower would travel foward and ding the aluminum frame. It was the bottom lip on the follower that was hitting. There is nothing to keep the follower from going foward, (poor design,IMO), other than that, the mags work fine. I have since ordered new followers.