M4, HK-416, SR-556, and now SIG-516?

[Ermac]

Are pistons a gimmick? I don't know. I don't own a Piston AR. To be fair, the army is looking to upgrade the M4's reliability and a piston is a likely choice.

[Spades of Columbia]

Piston is only worth having in a full auto...otherwise a gas blowback is just as good at less money. Remember that a piston gets dirty too and its alot harder to clean. Plus, my two cents, Smith & wesson makes a awesome AR and they have the best customer service.