A tough one, IMHO...
The overall width of the top might would seem too broad for a taperered dress hat, even punched in and out.
The width of the brim appears too narrow, as if possibly trimmed back narrower (which would delete the officer's ribbon edge binding.
However, brims on originals are found from 3 inches to 3 1/2, and it may just be the angle and play of light.
Dunno, beyond speculation and a limited view with the angle and play of light and shadow. Could be. Could be something else.
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.