The .380 and 9mm use the front of the front edge of the case to locate the shell in the chamber...which means the 9mm bullet will not allow the slide on a .380 barrel to fully return to battery...VERY DANGEROUS!
The .380 bullet can sit deep in the 9mm chamber, and the firing pin may not reach it, although it could.
Here's a picture of the .380 in a 9mm chamber, and in a correct .380 chamber.
Too deep, unless the extractor holds it back. Not good.
Flush with the rear, as it should be.
He who smiles last....
Not anything to do with me,...but SWAGA referred me to it...and it is pretty funny: The Ballad of Ajole
17 HP's and counting.