Shine, your second-to-last photo shows some words stamped on the barrel. One looks like "J R COOPER"? What is the other word? Wonder who/what Cooper was...
A couple of years ago the Backwoodsman magazine had an interesting article on shotguns made from cut-down CW muskets. The author gave details on about seven very different examples, and said in the upper midwest they are known as "Sodbusters", after the homesteaders who used them on the Great Plains.
I've got one myself: a 1842 Springfield with 1853 stamping on the lockplate. The stock has been cut down, and unlike most "Sodbusters", mine still has the large musket nipple. The mainspring and hammer-fall are strong enough to split atoms!