The 9x21mm, developed to circumvent gun control measures, has become a mainstay among European competitive pistol shooters. Several European countries do not permit civilians to have firearms chambered in the same calibers used by the military. Responding to this restriction, Israel Military Industries developed a cartridge that gave shooters the advantages of 9x19mm ammo without violating existing gun control measures. They made the cartridge two millimeters longer, and created a new non-military cartridge. The case is longer, but the bullet seats deeper in the longer case – making the new 9x21mm the same length overall as the 9mm Luger cartridge. The biggest advantage is that firearms already chambered for the 9x19 did not require any major modifications. Instead, a simple swap of the barrel was all that was needed to allow for the different length of the case.
The 9x21mm cartridge enjoyed another advantage upon its release – the United States Practical Shooting Association (USPSA) didn't permit the use of 9mm Luger as a Major Power Factor cartridge, due to the generation of unsafe pressures. The 9x21mm achieved Major Power Factor velocities without the dangerous consequences of the 9mm Luger handguns of the time.
Muzzle energy of 400 foot pounds, muzzle velocity of 1,250 feet per second with a 123 grain FMJ bullet, and a velocity of 1,300 feet per second with a 115 grain bullet is what you can expect from the 9x21mm. But the cartridge lost many U.S. shooters when the .38 Super arrived on the scene, and the USPSA allowed 9x19mm to reach Major Power Factor in open division pistol competitions.
The 9x21 is popular still in Europe – especially among those who shoot competitively. Glock, as well as many other manufacturers, continue to produce handguns in this caliber with no signs of demand dropping in the near future.