5.7mm Spitfire

.22 Spitfire
.22 Spitfire with FN 5.7×28mm and .30 Carbine cartridges
Type	Rifle
Place of origin	USA
Production history
Designer	Melvin M. Johnson
Designed	1963
Manufacturer	Johnson Guns Inc.
Specifications
Parent case	.30 Carbine
Bullet diameter	.224 in (5.7 mm)
Neck diameter	.253 in (6.4 mm)
Shoulder diameter	.332 in (8.4 mm)
Base diameter	.353 in (9.0 mm)
Rim diameter	.356 in (9.0 mm)
Case length	1.29 in (33 mm)
Overall length	1.65 in (42 mm)
Rifling twist	1:14
Primer type	Boxer small rifle
Ballistic performance
Bullet mass/type Velocity Energy 40 gr (3 g) 2,850 ft/s (870 m/s) 720 ft·lbf (980 J) 40 gr (3 g) 3,000 ft/s (910 m/s) 795 ft·lbf (1,078 J) 50 gr (3 g) 2,700 ft/s (820 m/s) 810 ft·lbf (1,100 J)
Source(s): Barnes & Amber

The .22 Spitfire (also known as 5.7mm Johnson or MMJ 5.7mm Johnson) is an American rifle cartridge.

Designed by Melvin M. Johnson of Johnson Guns Inc. for their conversion of the M1 carbine, this wildcat was introduced in 1963. It was based on the .30 carbine, necked-down to .22 (5.7mm).

It is suitable for rabbits, coyotes, or other varmints, and has potential as a military round.