I have had the same issue with several of the Ruger MKIII 22/45's. I have found that the magazines will not seat reliably by pushing them straight up, even if you push hard. You can tell they are not seated properly by feeling the magazine release on the right side of the frame. If the magazine is not engaged the mag release will not be flush on the right side. I have found that if I push the mags forward (toward the barrel) while pushing up they seat every time. I have not removed the mag disconnect safety on mine yet, but I am planning to. Hoping that mod will correct this issue.
