The .22 Spitfire (Originally the Johnson MMJ 5.7mm Spitfire, also known as 5.7mm Johnson or 5.7mm MMJ) is an American

wildcat The wildcat is a species complex comprising two small wild cat species: the European wildcat (''Felis silvestris'') and the African wildcat (''F. lybica''). The European wildcat inhabits forests in Europe, Anatolia and the Caucasus, while th ...

rifle cartridge developed by Melvin Johnson. In 1963, firearms designer Melvin Johnson developed a conversion of the

M1 Carbine The M1 carbine (formally the United States Carbine, Caliber .30, M1) is a lightweight semi-automatic carbine that was a standard firearm for the U.S. military during World War II, the Korean War and the Vietnam War. The M1 carbine was produced ...

to the Johnson MMJ 5.7mm Spitfire Cartridge, The cartridge is based on the

.30 Carbine The .30 Carbine (7.62×33mm) is a rimless carbine/rifle cartridge used in the M1 carbine introduced in the 1940s. It is a light rifle round designed to be fired from the M1 carbine's 18-inch (458 mm) barrel. History Shortly before World W ...

cartridge, necked-down to .224 (5.7 mm) caliber.Barnes and Amber, p.127. Originally designed with a 1-in-14 twist barrel, the 40 grain .22 Hornet bullet was the standard load. It could also be loaded with lighter or heavier weight bullets available at that time for the .22 Hornet as well as most bullet weights up to 50 grains such as that used by the

.222 Remington The .222 Remington or 5.7×43mm (C.I.P), also known as the triple deuce, triple two, and treble two, is a centerfire rifle cartridge. Introduced in 1950, it was the first commercial rimless .22 (5.56 mm) cartridge made in the United Stat ...

(5.7×43mm). The conversion is essentially a .22 caliber (5mm) barrel fitted to an

receiver with an appropriate feed ramp for the caliber brazed or welded into the receiver. Some commercial production

s were originally manufactured in this caliber with the feed ramp for the .22 Spitfire integral to the barrel. The specifications tend to land the cartridge about halfway between the

5.56×45mm NATO The 5.56×45mm NATO (official NATO nomenclature 5.56 NATO, but often pronounced "five-five-six") is a rimless bottlenecked intermediate cartridge family developed in the late 1970s in Belgium by FN Herstal. It consists of the SS109, L110, an ...

and the more recent 5.7x28mm FN. 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 3050 ft/s (930 m/s), though handloaders 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). In comparison, the "standard" load for the

has a .30 Carbine ball bullet weighing 110 grains (7.1 g); a complete loaded round weighs 195 grains (12.6 g) and has a muzzle velocity of 1,990 ft/s (610 m/s), giving it 967 ft⋅lbf (1,311 joules) of energy when fired from the M1 carbine's 18-inch barrel. Johnson advertised the smaller caliber and the modified carbine as a survival rifle for use in jungles or other remote areas. It was light, and easily carried ammunition in a light, fast handling carbine with low recoil.Barnes, Frank C., ed. by John T. Amber. Cartridges of the World (Northfield, IL: DBI Books, 1972), p.127.

Notes

References

* Barnes, Frank C., ed. by John T. Amber. "MMJ-5.7mm", in ''Cartridges of the World'', pp. 127 & 143. Northfield, IL: DBI Books, 1972. . Pistol and rifle cartridges Paramilitary cartridges Wildcat cartridges {{ammo-stub

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References