The .22 Spitfire is an American wildcat rifle cartridge developed by Col. Melvin M. Johnson.

[2][3] Originally designed with a 1-in-14 twist barrel, the 40 grain .22 Hornet bullet was the standard load.

Some commercial production M1 Carbines were originally manufactured in this caliber with an integral feed ramp for the 5.7 MMJ.

[6] Ballistically it is very similar to the rimmed .22 Hornet, but fashioned in a rimless cartridge design appropriate for a self-loading carbine with very light recoil.

The Spitfire M1 Carbine originally was advertised as firing a 40-grain (2.6g) bullet with a muzzle velocity of 3050ft/s (930m/s), though hand loaders with careful selection of modern powders and appropriate bullets consistently safely exceed those numbers while remaining within the M1 Carbine's Maximum Pressure rating of 38,500 psi (265 MPa).