Well about the only one that comes to mind is Obermeyer Rifled Barrel in Bristol, WI. Back then which was around 1976 I had a post 64 Winchester Model 70 that I used for both hunting and Metallic Silhouette matches. Anyway at around 1000 rounds out the barrel the barrel gave up the ghost. Winchester's answer at the time was that 1000 rounds was several lifetimes of shooting for the average person. I have never claimed to be average. I had Boots Obermeyer make me a 26 inch stainless steel super match grade barrel and had Earl Liebetrau from Black Earth, WI install it into the action of the Model 70 with a 7.62 x 51 chamber. Yes 30-06 down to .308/7.62 which all the experts said I would have feeding issues due to the short round in a long chamber. Never happened, never had an issue with rounds chambering. I glass bedded and floated that barrel in the original Winchester stock and used it for silhouette shooting with a Redfield 3 x 9 Accurange/Accutrack scope for many years. Was it sub MOA? well when standing offhand and shooting at chickens sub MOA does help but being able to hold your position does one better. When benching the rifle it held 0.05 MOA using my homebrew 7.62 mm handloads and Nosler or Sierra 168 gr match bullets. So in response to your question about barrel makers I would highly recommend Obermeyer Rifled Barrels who are still in business in Bristol, WI.