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.
A previously seen example surrendered in Bogota: