9mm/.35 cal
 

If a 9mm is .35 caliber, then why isn't the .380 called the .350? Is .380 just a made up caliber? Is the diameter of a 9mm and a 9mm kurtz the same?

The back of the casing is .38 inches and that’s where the measurement comes from. The case tapers slightly for chambering down to around .355 inches. (the reloaders can probably answer this question with more detail)

The designers and manufacturers of cartridges are the ones that name them. There is little consistency in the way that they are named.

Sometimes they reflect metric measurements of the bullet and case. Sometimes the inch system. Sometimes it's completely unrelated to the bullet diameter (as with .38 Special). I expect that some of the naming is marketing related (the number is larger therefore the cartridge must be "better", etc...)

Some cartridges have multiple names depending on where they are manufactured and sold:

9mm short = 9mm kurz = 9mm corto = 9x19mm = .380 acp...

9mm Parabellum = 9x21 = 9mm Luger....

There are others like this... some have very different dimensions like the 9mm makarov cartridge, which has no relationship to the 9mm Luger cartridge.


You can find the actual specifications that have been standardized by SAAMI at:

https://saami.org/technical-informat...mber-drawings/

9mmK / .380 ACP is 9x17.
9mm Makarov = 9×18.
9mm Para is 9x19.
9mm IMI is 9x21.
9mm Mauser is 9x25.
Etc...