I am jumping down the rabbit hole too.
A true .380 cal is the 9.8mm Auto Colt cartridge. Bullet diameter is .380.The .380acp,aka,auto colt pistol,.380auto,9mm Browning,9mm Corto,9mm Kurtz,9mm Short,9X17mm,9mm Kratak,9mm Scurt has a bullet diameter of .355 like the 9X18 Luger/Parabellum round. Not to be confused with the 9X18 Makarov(.364 diameter) Put that .45 back in its holster. Right now I am late, am late for a very important date