Thanks again. Although I've never seen the Colt version, I understand they used the rifle length (20") gas tube, however others have typically used the carbine length gas system and simply mounted the A2 gas block a certain distance back form the muzzle. Of course the A2 FSGB functioned as a sight only, which is what I'm looking in to doing. I've heard there were lots of problems with the rifle-length system so this has sort of become the "norm" for the dissipator.