I should have finished the sentence: a 380auto is the same diameter AS A 38 Special, a 9 mm and a .357 magnum, or within a thousandth of an inch.
The “rimless” 380 is held in the chamber by the rim of the case where the bullet is seated. This is how the rimless 45ACP round is positioned in a 1911auto.
The 380 cartridge won’t fall through a 9mm or 38 because the brass case is .374 outside diameter.
The diameter of a chamber of a 380 barrel is slightly larger than .374 so the cartridge will fit in and rest against a .010 inch-high shoulder at the start of the barrel rifling.
Well, it said the primer was dented but the rounds didn’t fire, so I’m thinking it didn’t hit hard enough because it wasn’t held in place by a rim.
“The “rimless” 380 is held in the chamber by the rim of the case where the bullet is seated. This is how the rimless 45ACP round is positioned in a 1911auto.”
Actually the .380ACP and .45ACP are head-spaced on the case mouth, not the rim. Just my $.02 worth...