Neal?

I had never heard of this. Found going down the wiki rathole about Personal Defense Weapons.

Instead of the M1 Carbine, which eventually prevailed, support troops would have been armed with a 5 barreled .22 with an insane rate of fire.  The development was slow, and not patented until after the war, so who knows if there is even a model extant.

The Neal SMG.

 I seem to remember Farmer Frank being leery of full auto .22.   Things can go wrong, badly, with rimfire at such a speed.  Dangerous to the shooter wrong.