I have a couple of them - better than common grade, very good rifling and both of mine shoot straight!
One of mine is a .58 with a massive 1-3/16" octagon configuration.
The other is an octagon 40 cal.
My wife shot a '63 Springfield with a Numrich barrel for years till it was worn out. As near as I can tell it was every bit as accurate as it now is with the Hoyt reline and as good as my Hoyt relined '61. I have another, a flush plate Whitneyville, with a Numrich barrel and it's deadly and I have set aside a nearly mint '63 Numrich barrel for when I need it. The supply of good Numrich rifle-musket barrels has pretty well dried up but they were held in high regard among skirmishers when they were available. I have a few Numrich round ball barrels for future projects and I expect them to be as good as anything out there. I would feel confident going up against any other barreled gun with a Numrich barrel. Look at the posts on how well their underhammers shoot. We don't hear much about them nowadays because they are not so common anymore.
I have found them to be inconsistant, some were very accurate , some not so good.Some had the bores not centered to the O.D. The one thing I found in them was that they were undersized on the bores compared to others. For example my 45 caliber liked a .435 ball and was too tight with a .440.My Hopkin and Allen swivel breech has Numrich barrels and it is very accurate!