|The idea for a lite machine gun in .22 caliber did not start with the
FN P90 in 5.7x28mm, which is a hot item today, in 2011..
It started way back in the 1960's. One of them was the 5.7x33 Johnson
Spitfire, (.22/.30 Carbine) designed by a Boston lawyer
and Captain in the Marine Corps Reserve named Melvin Johnson Jr..
Mr. Johnson turned away practicing law, to his passion, cartridge / rifle
design earlier in 1937 to designed, built, and successfully tested both a
semi-automatic rifle and a prototype light machine gun (LMG).
One of his last postwar ventures was in 1963, when he introduced a
5.7 mm caliber version of the M1 Carbine, aka "the Spitfire".
Johnson promoted the smaller caliber and the modified 22/30 carbine as
a survival rifle for jungle or other remote areas.
While the concept had some military application when used for in the
selective-fire M2 Carbine, it was not pursued and very few 5.7mm
Spitfire carbines were produced.
This is basically a military Wildcat, or now a
proprietary cartridge as a few have been produced commercially.