Re: .17 rem build ?s
I've built several 17 remmy's on the ar platform, and if you are going with a 20" barrel and a standard gas tube length, start SMALL on the gas port and work your way up. Standard gas port diameter is around .092-3" for a 223, and if I remember correctly, I had full function at around .075 or .078" in the 17 Remmy...that may have been with an 18" barrel and mid-length tube though now that I think about it. As for the gas port in the groove, if it is a 6 groove barrel, good luck fitting a gas port in the groove on a .17 cal barrel. I've done it both ways on the 223's and 6.5 Grendel, in the groove and where ever it may land. I have not seen any accuracy or fouling issue either way. Your choice but I just thread the tenon, chamber, and torque the barrel extension on and drill the hole where it needs to be. No trouble getting sub 1/2 MOA AR's using that method. IF you want to time the port, use your borescope and slide it up to where the port will be located, and mark the barrel tenon with a sharpie at every groove. When you thread the tenon, it is a simple matter to time the top of the barrel extension to one of the grooves.