They made it. I own one. USAS-12Deviating a little, within my family, we/they had blueprint and design of a Korean shotgun that was recoilless. Keep squeezing (or hold down) and it would shoot double 0s into the same pattern. Saw film demonstration of it shooting a hole into cinder/concrete blocks that the shooter walked thru the hole shot into the wall after one clip. Patent office and Firearms would not give permission to manufacture the guns in the US - too much killing power was reason given for turn-down.
I thought it would be a hell of weapon to take into a drug bust or close range military ckirmish.