Hello,

I just recently purchased the M&P sport 2, A.R. 15 chambered in 556 with the front A2 fixed sight. I’m looking to replace it with just a Picatinny gas block. However, I’m having a hard time finding what the right size barrel diameter is. I know they change the barrel to a 1/9 twist, don’t know if this has any effect on the barrel diameters outside dimensions. Can anyone hear help?

TT