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http://www.sandygunworks.com/Articles/The57JohnsonSpitfire.aspx
I was recently made aware of the .22 version of the M1 carbine developed in the early 1960s made by necking down the existing M1 carbine's .30 caliber cartridge with a 5.7mm bullet on the end achieving an intermediate assault rifle cartridge velocity of between 2700-3000 fps. With the M2 carbine automatic conversion it seems to me that the M1 Carbine could have been a genuine assault rifle in WW2, perhaps predating the StG 44 had right ideas been had. The smaller round is a minor modification to the existing weapon and making and automatic version is a mechanism modification, otherwise it would be basically the same weapon that existed in 1941. How could we potentially get an automatic 5.7mm necked down version of the M2 carbine ready for WW2? What impact would such a weapon have had?