I used a Troy  .750 LP Gas Block. If you don't have a DPMS tool take your M&P 10 to your local gun smith and have them change your barrel nut for you. And make sure the gas block is tight to the barrel flange.

Make sure you use the Troy 13.8  TRX 308 Extreme DPMS LP - BLK (STRX-E3D-13BT-00).

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US Army, SFC, Retired
DustOff