I have found that my Kimber ultra carry, which performs flawlessly with the mag. that came with it, will lock the slide back about every 2nd shot with a gov't length Chip McCormick shooting star mag. The CM mags. are flawless in my Stainless 2. Is there normally a difference between officer and gov't mags. other than length? I can tell the top of the CM mag. is made differently at the top and that my full length Kimber mag. looks more like the ultra carry mag., although I have not tested it for reliability.