I recently read some literature on a semi-automatic pistol that indicated it took ".380 auto" ammunition. When I examined pistol at a gun shop, "9 mm short" was stamped on the frame. Does this mean that two versions of the gun are available in different calibers, or are these two calibers interchangeable? The gun store clerk didn't seem to have the answer - and the two types of ammo were not available for side-by-side comparison. Thanks.