I've had good luck with the Stag BCG's but I agree that CMT needs one.

I have a older Stag lefty rifle with a JP barrel. Pretty sure I have the old Stag barrel somewhere. Need to look at the extension.

I also have CMT uppers with Daniel Defense, Noveske, Rainier and Ballistic Advantage barrels that run flawlessly. I did have an issue with a Stag bolt not headspacing with the DD barrel but another one was well within spec. They swapped it out with no questions asked.