The .22 ILARCO, also referred to as the .22 Winchester Short Magnum Rimfire or .22 American was an experimental rimfire cartridge developed by Winchester in 1987 for the American-180 submachine gun. At the time of development, the American-180 design was taken over by Illinois Arms Company, resulting in the name ".22 ILARCO", but as was noted above, it is known by a number of other names as well.
Development & Failure
Following Illinois Arms Company's purchase for the rights to the American-180, they believed that a more powerful cartridge than the .22 Long Rifle would be a better fit for the gun, especially when marketing to law enforcement agencies and other organizations.
According to "Aaron" in a thread at the Cartridge Collectors Forum from 2010:
"It is basically a hot-loaded .22 Long Rifle round, with the heavier bullet of the .22 Winchester Magnum Rimfire round and a strengthened .22 Long Rifle case with much more propellant. This was done to increase the power of the American-180, which could not chamber the longer .22 Winchester Magnum Rimfire round, without having to redesign the action and magazines. The power is almost the same as that of the .22 Winchester Magnum Rimfire. The .22 ILARCO round never went into large-scale production, and the sale of the American-180 patent ensured this. The .22 ILARCO is now a collector’s item.
Frank Barnes notes in his book Cartridges of the World (specifically the 16th edition), that the round utilizes a 40 grain FMJ bullet, an unspecified amount of "FL" powder, and achieves a muzzle velocity of 1.350 feet per second for 160 ft lbs of energy. This is apparently Winchester's factory load. Although the information provided by "Aaron" in the section above claims that this cartridge achieves similar performance as the .22 Magnum, this doesn't appear to be the case. In fact, Winchester's factory loading is actually weaker than modern high-powered .22 Long Rifle loadings such as the CCI Velocitor...
|Bullet Weight / Type||Powder Type / Amount||Velocity||Muzzle Energy|
|40 Gr. FMJ||"FL" - Unknown amount||1,350 fps||160 ft lbs|