I've chambered a few blanks for service rifle competition and other projects. One of my good friends, a hm, said he shot a personal best at 600 with. I have also had a few that shot good but nothing to write home about.
They are a good decent barrel
Green Mountain as a brand has been around a long time, in this industry if they weren't any good you'd have heard it by now. I have one of theirs on a 10/22 and it is good to go.
i have a yugo M70AB AK47 that has a green mountain barrel and it shoots 2" groups at 100yds with a red dot sight and very old eyes , i am a satisfied customer and give them a thumbs up.