As a collector of percussion over under guns, I've got a bunch of them by Barry C Wood of Painted Post, NY. MOST use one back action lock, which fires the top barrel, and an underhammer lock to fire the bottom barrel. They were made with both barrels rifled or with the bottom barrel left smoothbore. Mine, with two back action locks as your gun, is .42 rifle over .50 smooth. Yes, the rifling handles patched lead balls well. Yours seems a bit "rough", so I wouldn't want to fire it without a very careful inspection by a qualified individual... Barre Cole Wood was born in 1817. He moved to Painted Post in 1840 and died there in 1902.