One mystery that consistently driven me a bit crazy is the subject of whether BUL M-5 Ultra magazines are compatible with the BUL Impact, and vica versa. I finally have an answer. As you can see in the above picture, the difference between the two magazines is the follower. The Impact magazines (seen on the right) have a slightly different follower with a higher left hand side to push up the Impact’s slide stop. The M-5 magazines (on the left) have a “normal” profile follower without the raised edge. You can use either magazine type in either gun, but the M-5 magazines won’t actuate the slide stop on the Impact, and the Impact magazines will require more force to release the M-5’s slide on an empty magazine.
Given that proper Ultra-X magazines appear to be going for astronomical ($100+) prices these days, being able to use DDA mags should be very financially helpful to owners of the Charles Daly M-5 Ultra-X and the Kimber Ten II Ultra.