I’ve only seen two guns that I could honestly say were most likely built as barn guns. Ones finish I would suspect was sweat, and dirt, on the wood, and what appeared to be linseed oil put on the metal parts after they had been heated hot. The other one had barn red paint on the stock, and what appeared to be shellac over the metal and the barn paint. Both were no bigger than about 40 caliber, but only one was rifled.
Hungry Horse