Not as made or issued.
IMHO, most likely a sold as surplus and then "personalized" by its owner who either did not like the three leaf military sight, or the orignal sight had been taken off and lost. And, a newer "block" rear sight was added to the preexisitng rear sight dovetail.
Many times, these were also bored out and sold as "poorman" or "farmers' low-cost shotguns, and the rear sight was removed and replaced by a dovetail insert and filed and polished flush with the barrel to be nearly invisible.
It would also appear that the post War owner did not like sling swivels...
In gleichem Schritt und Tritt, Curt Schmidt
Not a real Civil War reenactor, I only portray one on boards and fora.
I do not portray a Civil War soldier, I merely interpret one.