Looks to be like one of those hellfire deals...a spring / cam mechanism mounted to the triger guard. 1 round fired for each triger pull...the recoil keeps it going. You pull the gun foreward and away it goes, up, got to hold it down. The law is just that 1 round / 1 triger pull. They are about $25 around here, they work quite well with the 7.62 x 39 and .223 anything bigger, .308. I have seen people try them on a 9mm it just take adjusting the cam tension. I had a 100 drum go through a mak-90, it is close enough to full auto for me...puts a smile on my face every time.