Reply with quote #9
I used a borescope to locate the groove, it could be done with a lead slug attached to a cleaning rod. I drilled the gas port hole with a lead slug in the bore to leave a clean hole, I also started with a smaller pilot hole. The hole is definitely a disturbance in the bore, I don't know which is better.
Reply with quote #10
I was gonna suggest that idea: lead slug "indexed" as a tell-tale to a rod of some sort; measure back to a point on the rod so as to reference the groove position on the slug when it's at the proper point inside the bore, then mark the barrel for drilling.
Hesitated as this is all theoretical to me: I do far better working wood than I ever have working metal, in any capacity.
Reply with quote #11
I've chambered and installed quite a few AR barrels in the last 5 years, and if I really want the port in the groove, I'll measure from the breech end to the port location and using the borescope mark the breech end of the barrel with a sharpie w/ the locations of the grooves. When the tenon is turned and threaded, I can face off the shoulder a whisker to index the barrel extension properly so the port does end up in the groove. Honestly I don't think it makes a difference, but some customers want to be assured it's done that way. Usually I just chamber and thread, and drill the port w/ a jig of sorts that uses drill bushings. I start with a SHARP drill bit at least .010" under target diameter for the initial hole. If it's a barrel length and caliber I'm not as accustomed to, I'll test fire as I incrementally increase the dia. of the port to assure proper function without over doing things.
Reply with quote #12
I have also seen evidence of peening of the gas port where ever the port is placed. I can't comment on the 50/50. Chamfering the port on the exit side does help. You can also lap the barrel after a few hundred rounds to help with fouling. Lothar Walther blanks seem to be less of a problem than others I have seen.