Gun is percussion. As near as I can see without a bore scope or the like but with a pencil Maglite from muzzle to and including the breech face both barrels look like chrome plating today, mirror bright and smooth. As near as I can measure with "mics" the left barrel is the thinnest measuring .030, .032 and .034 at 3", 6" and 9" respectively. What is a safe limit?