I believe the Ruger AR-556 is DI gas operated.
Looking to get another AR15 and would like to get a Gas Piston driven model.
I have the Sport which is Direct Impingement gas driven and I have had no problems.
Just curious if M&P makes a Piston model.
Gas piston ARs are a bad idea. The piston causes the bolt carrier to damage the inside of the receiver over time and the damage is not repairable.