Last time I counted, there were ELEVEN different 9mm cartridges still extant. Some, like the Makarov, are NOT 9mm (9.3mm), but are called 9mm, while others ARE 9mm but have different names (like 38 ACP).

Sizes range from 9X17 through 9X23, with some sizes having different pressure loadings, but the same external dimensions.

In addition to the eleven, there are the overpressure loadings designed for competition guns only, like the "major 9mm."

It's not safe anymore (if it ever was) to pick up somebody's lost 9mm off the range and fire it.