I have experience with both Green Mountain and Shaw barrels. The Green Mountain is an 18”, non-threaded, chrome moly, 0.920” barrel. The two Shaw barrels are (1) 18” chrome moly, 0.920”, non-threaded, and (2) 16.5” stainless, 0.920”, non-threaded and ordered through the Shaw custom shop when Shaw recently has a 15% off sale over Christmas. Keep in mind that three barrels is a tremendously small sample.
Eley Benchrest Semi-Auto Benchrest ammunition used through all barrels, at 50 yards, same or similar conditions, 10 rounds (because that’s what fits in the magazine). Flyers not counted. First round from magazine not counted, because I get more first round flyers than good shots. All barrels floated. I assembled all rifles.
The Green Mountain barrel shoots great, delivering edge-to-edge 10-shot groups, routinely, at 3/4” or less.
The 18” Shaw barrels shoots good, delivering edge-to-edge 10 shop groups, routinely, at 7/8” or less. This barrel shows definite tendencies for ammunition is likes, and dislikes. It dislikes Lapua X-Act, with over 1” groups. It loved the no longer made Federal UM-1(?)—the stuff made for the Olympics, which sadly, I have shot all of it—this particular ammunition delivered consistent MOA groups at 100 meters with it.
The 16” custom Shaw barrel shoots great, delivering edge-to-edge 10-shout groups, routinely, at 5/8”, and maybe one group in ten groups will be under 3/8”—I had to measure those groups twice. I even shot a 3/16” group, 8 rounds with two hilarious flyers. The barrel took five weeks from order to delivery, and came with “CUSTOM” on the side. I bore scoped it. Chatter marks are present and are of the same magnitude as the 18” Shaw barrel. Someone had polished the bore!