Thank you for the reassurance that it's probably not some old old antique. It has a steel butt plate which I hope appears in the pic I posted. I'm reluctant to scratch or file a bit of the finish on the trigger guard to find out what's under it, but it is mounted with two fasteners to a narrow steel plate that is let in to the stock. The front fastener is a pin, and the rear fastener is a screw with a slotted head that runs up from under the plate, holding onto the trigger guard with torque only.It looks more like an English scroll guard half stock rifle. Interesting that it has relatively flat shot gun style butt plate and a drum rather than a snail for the percussion nipple. It appears to have a nice pewter nose cap. The style is like a Henry scroll guard rifle. A Henry would have plenty of identifying stamps so I don't think that it's 150 years old.
What's the material for the butt plate, trigger guard, and thimbles for the ramrod? The trigger guard appears to be brass.
Any markings inside the lock plate?
It's hard to see how many wedges or pins are holding the barrel in the stock. I think I see two.
I don't know what it is but I like it. Would not be ashamed to have one like it in my small collection.