.22 ILARCO

The .22 Winchester Short Magnum Rimfire, also called .22 ILARCO, was a rimfire cartridge designed for the American-180 rimfire submachinegun. At the time the cartridge was created, the design of The American-180 had been taken over by the Illinois Arms Company, Inc. hence the ILARCO name.
History.
Sometime after the Illinois Arms Company, Inc. (ILARCO) purchased the rights to the American-180 they determined a more powerful cartridge would be appropriate which resulted in the creation of the .22 magnum short. The new cartridge was designed so that a simple change of barrel was all that was required required to switch between standard .22 long rifle, for which the gun was designed, and the new cartridge.
Dimensions and loading.
The .22 Short Magnum uses a shorter version of the .22 WMR case with the same 40 grain projectile as the original .22 WMR loading.