Ok so one if my dumb friends new to the AR (yes the panic buyer), got suckered into this short bolt carrier. I told him to hold off firing with it because I've never seen one like this. It was advertised as 556 bolt and yes he got raped for it I can't imagine it being safe to shoot, and thought it was either for a 9mm conversion, or some type of short stroke piston system but could use some confirmation. Thanks in advance gents!