Short Stroking in Subsonic AR15

[Fritzcat]

RobRat, the middle position on the gas block should be for sub-sonic, the rear position is for super-sonic, and forward for single shot. The gas block should have a C closed, M moderate, and H high. You can also verify by using some small drill bits and insert them in the gas tube hole. My middle position is .125. I am able to shoot 150 FMJ using Unique or Blue Dot. The 240gr and powder you have should shoot just fine.