It's definitely not a military piece. That said, quite a number of civilian arms were used, especially by Southern troops and by both sides in the trans Mississippi theater so any civilian arm of the mid 19th Century could have seen a battlefield. However what this appears to be is a post Civil War piece and as the gentleman above pointed out a cheap firearm for natives to use to shoot pigs and pigeons and not particularly lethal to the local constabulary. I had one of these guns 40 years ago, made in Belgium, about .36 caliber smoothbore ( it actually fired a .38 caliber slug). First class junk. If this guy insists it's from the Civil War I would advise you to think twice about his firearm expertise. I see them frequently at flea markets, and in much better condition. In my opinion it is neither from the Civil War nor an especially noteworthy addition to a gun collection.