I have a percussion double-shotgun made by JAS. DONN & BRO. CANTON ILLS. which was found inside an interior wall of a house being remodeled in Dubuque, Iowa.
Also~
About forty years ago I knew an elderly gentleman who had been an antique dealer for most of his life, beginning in the 1930's. He said he believed he had bought and sold at least three hundred muzzle-loading long guns for $3 to $5, before WWII. He told me that he had cleaned out the attic of a large victorian home, for an elderly lady, in exchange for the contents of the attic. When he thought he had finished, she told him there were three old guns down inside an interior wall that could be accessed from the attic. She instructed him to "get them out of there". He had to lie on the attic floor and reach his arm down inside the wall to retrieve them. Two were longrifles, which he was able to reach and pull up quite easily. The third was a percussion double-shotgun. It being shorter, he was just able to insert two fingers into the muzzles and thus pull it out. After he got it out of the wall and looked at it, he realized that both barrels were loaded, both nipples were capped, and both hammers were cocked.