1884(?) Trapdoor

Bought this today. Initially I thought it was an M1873, due to the breech block marking, but as I really got to looking at it, it appears to be an 1884 (These are a bit out of my circle) Serial number check, if correct, shows DoM of 1888.
The serrated trigger and Buffington rear sight first got my attention. The breech block is an 1873 marked 'low arch' version.
Stock has zero cartouches.
Barrel has no VP proof..however, there is a 'P' on the underside of the barrel. The only marking visible on the barrel is what appears to be a tiny 'R'.
Lockplate is worn. You can barely see the eagle and 'U.S. SPRINGFIELD'.
So what in the world do I have here? A rebuild? Bannerman's? Rock Island (I saw a thread that suggested they assembled some, don't know how accurate that was)
Either way, no rust, no pitting, very tight lock up with three clicks.
Check her out!

Nice looking old rifle, around here anything like that is priced out of reach so there's no chance to have one. They're scarce too...here.

The 1873 blocks were used until the supply ran out. There was no reason to scrap a supply of blocks whose only difference was the date on it. Common to find then up to 1887. You rifle looks like it has been together for a very long time and the parts finish is uniform over all. I would not worry about its family heritage .