Ok so I took my pt 1911 out today for some range time, and had a few times where the slide did not lock back on the last round. I was using two differnt magazines one was a kimber and the other a chip mc cormick shooting star. I never have had a issue with these mags before, the chip mc cormick is one of my favorites. So my question is, what is causing this? Is it the mags or can it be somthing within the pistol? Thank you all for any advice.