Can't see what the mark is? That's because we sanded them off, perhaps the floor plate on some are welded into the tube upside down...a lot of them were the Detonics 45 floorplates, welded onto shortened 9mm and 38 super mags. The orig. 9mm mags also had a spacer in the rear of the mag, so the bullets did not shift back so far on recoil...John