Underhammer punt gun from 1870s
This monster punt gun, dating back to the 1870s, weighs about 100 pounds and is 6ft. and 4 inches long. It has a bore size of 1.5", which puts it somewhere between 1.5 Bore (1.459") and 1 Bore (1.669") in size.
More information about it at The Underhammer Society.

Interesting; I’ve never heard of a shotgun or puntgun referred to as “bore” since pounder/gauge were the standard for centuries. I’d guess this one was just made at a conveninent diameter but still expect it was a 1 pounder for it’s square load.
Anyone have some good sources (books) to read up on puntguns?