I posted the pics on the ASSRA forum. General consensus was that it was a barrel in which something went badly amiss in the rifling process. From a Green Mountain barrel. I don't know how it was rifled (button, etc) but the collective opinion was that something happened to the part that was cutting one land. One comment said that if that happened, the cutter would make a screaming noise that could be heard throughout the shop.
Whatever happened, the rifle, a Low Wall in .25-20 WCF, is only capable of paper plate accuracy at 100 yards.
My thought is to put a TJ liner into the barrel and turn it into a 22 LR.
I have an extra Winder. Will a Winder breech block and a Low Wall breech block interchange? Both are originals. If I could swap them, I would get the Winder bored out to some CF caliber, maybe 25-20 SS.