Question is why the comparison? To begin with you could not trim a 9mm down to use it for 380, its too wide. And a 380 wont headspace in a 9mm since it headspaces off the mouth and its too short.
Confusion may be created by the relatively long list of alternate names: Other names for .380 ACP include .380 Auto, 9×17mm, 9mm Browning, 9mm Corto, 9mm Kurz, 9mm Short, and 9mm Browning Court