Someone asked about the wood type, and judging from the 5th picture down, it looks like curly maple. That would be the typical wood for the time and likely being made in Penn. The black is just the old finish ageing/oxidizing with time.
Whether or not its a Shreckengost I can't say as I'm not that familiar with their work. However it does look like a typical rifle made about 1850 to about 1870, and of course could have been made on either side of that date.
Percussion locks with a pheasant, quail, rabbit or flying ducks must have been really popular, as they're seen on lot's of rifles of the period. It looks like it was a higher quality gun to begin with as the butt plate was silver plated and still has some remaining. I can't see if the trigger guard is or was plated as well, be expect it was? None the less, its a popular style used during the time.
Whether or not your family member actually made the gun, or just added inlays to it might never actually be known, but doesn't really matter. It's been owned and cared for by your forefathers, handed down, and now its your turn! Can't ask for much more than that!
If it were mine, I'd just give it a light coat of furniture wax (Goddard's, Renaissance) on the wood and metal, an oily patch down the bore, and a few drops of light oil on the lock and trigger works, and enjoy it!
By the way, I live in La Mesa, and if you want to get together sometime, shot me an email or PM.
John