The double set triggers look to be of period style.
I have not seen a trigger guard with that hook spur, though.
There are a lot of half stock percussion rifles out there; it might be a repair with a split full stock cut back or it might have been made that way.
The inletting around the front of the lock plate looks rough, surfaces look patinated, hammer spur is not checkered.
I think it may be original but a plain, inexpensive gun not well preserved.
Not MY $999, for sure.
Edit: I thought about the possibility that it was a drum and nipple conversion from flint but the lockplate does not look long enough. Pictures are not good enough to see where a pan and frizzen used to be mounted.