This gun looks like some variant of a Perfected Single Shot, that has
the alternate barrel and cylinder, instead of a single-shot barrel. If
that is what this is, it is built on the 38 Perfected Double-Action
frame, according to the book.

What is the caliber of your gun ? I think the gun I describe above
is a .22 caliber, in spite of the frame that it is built on.

Judging from the edges of the side-plate, your gun has been
reblued.

Perhaps Ed Cornett will see this, and help identify it.

Later, Mike Priwer