I See Bullet Diameter of the 10mm is 10.16 mm (0.400 in) and the .45acp Bullet Diamter is .452 in (11.5 mm) So the .45acp is the winner in Bullet Diameter. The Case Length of the 10mm is 25.20 mm (0.992 in) and the .45acp Case Length is .898 in (22.8 mm) it seems that the 10mm is the winner in Case Length. Just wondering who is truly the more powerful round????? i got this info from wikipedia by the way there is more info on there. it's like 45acp vs .357 magnum the 45.acp is a larger bullet diamter but the .357 magnum holds a lot more powder in its case then the .45acp.