Well, I needed to replace the AR that got stolen the other evening and this is what I decided to replace it with. The ZM has a folding stock because the recoil spring is around the gas-piston beneath the forearm. There is a modified bolt that is driven by the gas-piston. This is a self-cleaning system that should eliminate the problems associated with the AR crapping where it eats. The delivery time is a little long but I'll post a range report when it gets here.