Isn't a chunk gun actually. It shoots conicals. Common descriptive vernacular is "slug gun".
It was built by D.A. Hilliard in the general vicinity of Cornish, NH. You can find information about him with a little Google-foo. It is alleged the scope was crafted by a fellow named Rice who was one of the first to build telescopic sights but I have no provenance on that.
.50 caliber, 16" twist with all tools. I have two moulds and hammer die sets, one for a 490 gr pill that vaguely resembles the old sugarloaf picket except it sports a flat base and does not have a radiused heel. The other is for a 650 gr slug. Gun weight is 19#, and that is fairly light for the class and caliber. It uses cross strip paper patch and in calm air has demonstrated ballpark MOA precision at 200 Yds. The bore is without flaw, something I find quite remarkable.
In response to you inquiry, the form of the hole for the nipple is full bore diameter into the chamber. There is no step.
DD
