The funny thing about a Colerain is that the outside is very rough and wavy, but the bore is exceptional. I've only used one in my builds, a short little .54 cal rifle for my daughter. I first cut off about a foot of barrel, then worked on getting the outside smooth and flat, and then used that dimension to cut the barrel channel. When I was finished, so much metal was taken off that the piece of original barrel wouldn't come close to fitting into the barrel channel. But, the accuracy is fantastic. It's round bottom rifled, easy to clean, and the best shooter in the family. I would get a Colerain over a G.M. any day (depending on avialability), I just know they require more work.
And the breech threads were very good also. Crisp, clean, cut right up to the shoulder.
With only one Colerain under my belt, I'm no authority, but others I have talked to mirror my experience. Bill