BudsGunShop.com - Used for what firearm?

Tony, as Paul stated, they do make guns chambered in this caliber. As it is a rimless round, the 9×21mm is used in USPSA/IPSC competition in open class firearms. A rimless case is preferred because, unlike semi-rimmed or rimmed cartridges, it will not tend to lock together with other rounds in a double-column magazine, resulting in a malfunction. As other .38 Super–based rimless cartridges became available, the 9×21mm decreased in popularity in the United States for competition use, but it is still widely used in the rest of the world.

No, this is not 9mm or 9×19. This 9×21 is a much hotter round, so has higher velocity and pressure. Like Paul said several manufacturers make firearms for this like Glock, Beretta, sig believe some 1911s and I'm sure more. They also have a 9×23 round Wich is even a hotter round. Hope this helps.

There are berretas, glocks, bul m5, rugers and sigs all chambered in this caliber , I typed a longer response with links and buds deleted it, so yeah just Google 9x21 pistols for sale they are spendy, and hard to find.

9mm is 9x19 this is "9x21mm imi"
The 9×21mm pistol cartridge was designed by Jager, then adopted and commercialised by Israel Military Industries for those markets where military service cartridges, like the 9×19mm Parabellum, are banned by law for civilian purchase by some countries in Europe and Latin America.