A development in improvised weaponry spearheaded by South America’s drug cartel armorers has been the blow-back operated open-bolt automatic rifle. The simple solution to the usual intricacies of a typical assault rifle’s locking, delay or gas operation is to essentially make a scaled-up submachine-gun with a very heavy bolt capable of operating at much higher pressures. Using a fixed firing pin and firing from the open-bolt position allows for relatively simple construction with minimal components. Police helicopters are rumored to be some of the intended targets.
Impro Guns 
Looks like the barrel is short on the .50 bmg for a good reason. With the short barrel, you might be more likely to get away with straight blowback in such a big caliber. I wonder if the ammunition had to be lubricated for the gun to work?
LikeLike