Whether you call it the 9x19mm, 9mm Luger, 9mm Parabellum, or 9mm NATO, it's the same cartridge. Same size, that is. Some military ammo is loaded hotter, and/or with harder primers, for use in submachineguns. Such ammo should be avoided for use in your average 9mm pistol.
Now, I don't mean to oversimplify things here. There are a host of other 9mm cartridges, which are not the same. These include the 9mm Action Express, 9mm Bayard Long, 9mm Browning Long, 9mm Centerfire (which is actually a shotgun shell, if you can believe it), 9mm Makarov, 9mm Ultra, 9mm Winchester Magnum, and 9mm Kurz (380 ACP) just to name a few.
It's worth reiterating that the cartridges in the paragraph just above this one are not the same as the cartridge which is the subject of this article, which many shooters refer to simply as "the nine," or "nine millimeter." Those cartridge names, again, are 9x19mm, 9mm Luger, 9mm Parabellum, and 9mm NATO, and they all describe the same cartridge.
No entry on this old cartridge would be complete without mention of the oft-repeated claim that "parabellum" means "prepare for war." Regardless of what you call it, this little round has been used in many armed conflicts all over the world, with its main advantage being that you can cram a bunch of them into a given gun.
This cartridge undeniably lacks the knockdown power of the delightful old 45 ACP military pistol round, but you can sling more of them downrange between reloads, and carry more of them with you while you're fighting your way through the crud.
- Russ Chastain