[DefenseReview received the following post-interview via email from John Noveske: "Also, we should mention the poor choice of platform for the piston conversion on a round receiver bore as found on the M16/M4 system. All other piston type systems out there utilize a railed receiver design, like the M14, AK-47, M249, FAL and so on. The round receiver bore design used on the M4 is only acceptable for the standard op system. The carrier and bolt expand on axis with the bore under the normal gas impingement cycle, but on a piston gun, you run into off center impulse issues with carrier tilt and incorrectly designed carrier contact points. Some designs attempt to address the carrier tilt problem with over sized carrier tails and rollers. I do not believe the receiver extension should be used in this manner.
Understand that even if you outfit an AR-15 carbine/SBR with a gas piston/op-rod, which the AR-15 wasn’t designed to utilize in the first place, you still have a round bolt carrier group moving/reciprocating inside a tight round tunnel in the receiver, instead of on rails, which is how it really should be done. So, you’re really only solving half the problem, if there’s even a problem to begin with–and that’s highly debatable. If you’re going to utilize a gas piston/op-rod arrangement, it’s best to design the gun for that system from the outset, rather than modifying or converting a direct-gas-impingement (DGI) gun to gas piston/op-rod operation. Check out a Kalashnikov rifle/carbine (AKM, AK-47, or AK-74) sometime, and see how the bolt group runs (slides back and forth) inside the weapon.
thisNOVESKE.