A couple corrections.

Originally Posted by
BGREID
The bolt does have piston rings on it.
The bolt design incorporates gas rings, not piston rings. "Piston rings" would lead a person the the incorrect logic that the bolt is a piston because it has seal rings.

Originally Posted by
HansTheHobbit
Yes, a piston has to move to be a piston.
Not necessarily, as a piston is only the inner fitting of a sealed chamber, where the cylinder is the outer fitting. However, it wouldn't be reasonable to use this to conclude the AR is a piston operated weapon, as the presence of one piston in an entire system does not dictate the entire system is a piston operated system.
A couple observations.
Impingement. To impinge is to directly strike, dash or collide with. This would imply the process of channeling gas into a chamber which is forced open by a rapidly increasing volume of gas cannot fit the definition of Direct Impingement, because there is no impingement.
This still doesn't show us that the AR design is piston operated.
More at 11.
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