Like the end product, hate the work. I've used them twice in my builds and each one has been VERY rough on the outside. Deep milling marks and chatter. It takes running a file longways to get the flats actually flat before you can start smoothing by draw filing. On one barrel, I cut off a few inches, then smoothed out the roughness, then used that dimension to cut the barrel channel. When the finished barrel fit nicely, the original untouched barrel piece wouldn't come close to fitting into the barrel channel.
But, the inside bore is very good. Both barrels had round bottom rifling and were very accurate. I don't remember either barrel having patch cutting issues when new. And with both, the max ball size was .010" under nominal size. The .54 was very tight using a .530 ball, as was the .58 with a .570 ball. With G.M barrels, I always use .005" under (.535 and .575)
Only two Colerain barrels under my belt, but I see a pattern here. As far as shooting them, I think they're better than G.M. As far as the building part, start with a rough file :grin: . Bill