Originally Posted by
Southern_Partisan
You can't pin a gas block on the Mega. You have to first torque down the barrel nut, and then slide a set screw-type gas block into place and tighten the set screws through the elongated hole machined in the underside of the quad-rail. You have to assemble in this order because the barrel nut wrench will not fit over the gas block. Pinning a gas block would not be a problem with the VIS because the lower portion of the rail is removable as noted earlier.
I had sent my components to Adco to see if they could pin my Vltor low-profile gas block. They did a trial fit and found that they could not properly access the gas block through the holes in the rail for pinning (the angle wasn't right and they couldn't drive a pin straight in). The BCM BFH 16" mid-length barrel I used for my build came with one dimple, so I had them install a second dimple. I was advised by rob_s that Rocksett is less prone to degradation due to heat than Loctite, so that is what I had them apply to the set screws to attach the low-pro.