It is- but a 9mm is a metric round. The .38, .45 (not called the 11mm commonly in metric..)
.22, .44, and 357 magnum are all examples of common non metric sized rounds found in pistols. As a fun asides- the 357 magnum cartridge is about 9.1mm but you won’t find many metric users calling it the 9.1mm magnum or even “9mm magnum.” Very slight differences in a round can produce profound impacts on performance or ballistics though- so it isn’t generally wise to assume that two rounds are comparable because they share certain dimensions sure- but to the larger point the use of metric to refer to metric rounds by name makes as much sense as the use of non metric rounds not being called their metric sizes in metric countries. Plus that could cause severe confusion with existing and more common metric rounds that have a close standard equivalent.
For sure, I was just kinda being a shithead. Lots of cartridges share a similar or even identical bore size all the while being completely dissimilar in ballistics.
Lol. Nah. I’m with you on that. It’s just a fun fact. Like. 7.62 and .308 being the same size more or less with different shoulders. And that’s a round that (unless a weapon was designed to fire both,) sometimes can be swapped and sometimes can’t- depending on the direction you’re going. And I mean- you mentioned a .38 being a 9mm more or less and the 357 magnum is a longer more powerful bullet- but a 357 can safely fire a .38 special and some .38 specials can UNSAFELY fire a 357 if they have a long cylinder.
So I wasn’t hating on you, just joining in the fun. I mean- you have a valid point. The round is usually named by whoever originates it, so metric countries design metric rounds by and large- but even in the cases where a country uses a different unit to label a round it is usually because the round itself is too close to an existing round in dimensions, so they use another label to identify it. The .38 and .357 magnum were originally more or less the same round- a hot .38, not a problem when all guns are overbuilt but crackers, but a lighter frame non magnum can suffer catastrophic failure running hot rounds so they lengthened the case of the .357 to avoid accidents.
Designations like “magnum” or SMG etc are often used in such cases, with 9mm being a common pistol but also SMG round, and many older SMG using a “hotter” 9mm for reliability of the action. A tank like an M92 beretta will chew and spit hot rounds all day, but most tactical Tupperware like an older standard glock 9mm won’t appreciate a hot round for long.
.22, .44, and 357 magnum are all examples of common non metric sized rounds found in pistols. As a fun asides- the 357 magnum cartridge is about 9.1mm but you won’t find many metric users calling it the 9.1mm magnum or even “9mm magnum.” Very slight differences in a round can produce profound impacts on performance or ballistics though- so it isn’t generally wise to assume that two rounds are comparable because they share certain dimensions sure- but to the larger point the use of metric to refer to metric rounds by name makes as much sense as the use of non metric rounds not being called their metric sizes in metric countries. Plus that could cause severe confusion with existing and more common metric rounds that have a close standard equivalent.