I guess it’s all about context, could these three men have served as confederate soldiers!
Could it not be that this is either an earlier or later photo of three confederate comrades. It would be interesting to know exactly what Information the museum displayed about the photo.
I would put this at least 20 years postwar, and at that they all look too young to be CSA veterans. The uniforms look much like some favored by some fire brigades. But what they'd be doing with shotguns, I don't know.
After the war beyond a doubt. The leggings look to be much more modern, and maybe khaki, such as in Military issue. I would guess the image is closer to the 1890's. The backdrop is pretty crude, and the shotguns could be props.
Those ties date it, too- once drove myself a little crazy trying to pin down when men did that to themselves, that specific knot, I mean. Never did discover exactly when but seem to remember it was several decades post-war?
Looks like circa 1890's. In Flickr veterans of the American Civil War we'd get photo submissions from the post war period or from Europe. There's an admin in the group from Europe who knew the European uniforms, his name was Fred Hall. Ron Coddington is also a group admin who's written several books based on civil war veterans photos.