Here's food for thought:
The direct impingement system is in virtually all the M16 in the field today with our Army. It has been there for 50 years. If it were a problem don't you think maybe the Army would have done something about it.
Direct impingement system becomes a problem with a short barreled gun as the pressures are too high so close to the chamber and very difficult to control to get repeatable results so those gun gain something with the short stroke piston operation.
When you convert a direct impingement system gun to piston operation the forces on the bolt change significantly. in the direct impingement system the gases enter the key on the bolt and expand the bolt internally to unlock the bolt.The forces involved are basically on the centerline of the bolt.
When you convert to the direct impingement system, the rod, driven by the piston at the front of the gun, operates on the end of what was formally the key on the bolt. The key is several tenth of an inch off the centerline of the bolt which tends to cock the bolt in the receiver. The receiver rails are aluminum and were not intended to have that force from the cocked over bolt operating on them. This has to increase the wear on the aluminum receiver and on the bolt body. Add to this that a regular key is a attached appendage to the bolt body and now that connection of the two parts has to absorb all the force required to operate the bolt. Sheared off keys might be in the future for a converted gas piston gun.
As I said this is all just food for thought. I would never ever convert my AR15 to a gas piston operated gun! These conversion are just a fad.
LDBennett
