I've looked at this barrel in person and it has all the appearance of a clean cut. It looks as if a boring bar was run a 1/4" down the barrel. There is even a very slight shoulder at the end of the marks. I've seen what centers do when they gall, and this doesn't look anything like that. The crown also looks to be cut with a lathe rather than a crowning tool. It is very puzzling to stare at.

I will second that the gun is a hammer with match ammo.