I have a fairly plain Gye & Moncrief hammer gun which was given to me in the 1970s. It looked as if had been "reamed" to 28 gauge, from a double rifle. It had a short section of rib at the action, but with no obvious provision for a sight. At the muzzle, the barrels are banded together, again, no obvious provision for a sight.

The late H A Clifton lined it to .38-55 for me while he was in California (later in Bellingham, WA). David Yale added a front sight and a tang sight on the wrist.