imported post
SpyderTattoo wrote:
This doesn't sound like the right kind of subject for this forum. Might want to take it to the General forum or the AR15 forum.
He's right.
But to answer your questions:
Direct impingement allows the mechanism to move backwards as perfectly straight as possible, which prevents warping, scoring, etc. Downside is that because the gas is delivered directly into the bolt carrier group, it's dirty.
Gas piston is cleaner, but because of the way the piston pushes the mechanism back it stresses it because it's being pushed at an angle. Most weapons such as the SKS and AK have their bolts made so it can compensate for it.