Wow, that certainly is a head scratcher. I agree, evidence supports that it's probably a pieced together rifle. I found Fred's original thread. That #6 is NIIICE!
One question: The #6 rear sight has two peep holes, my friend's gun has one. Is that another variation of musket sight or possibly something Bannerman made?
I've asked my friend to take some more detailed pictures and check the trapdoor date and look for any other markings, but barring any interesting findings I'm pretty convinced it's a put together.
Sadly enough, he had it appraised at a VERY well known gun shop a few years ago (2011). They called it a 2nd Allen and put a $600 appraisal on it. If I could pick it up at a reasonable price I'd add it to my collection all the same, but I wouldn't want him to think I was lowballing. We'll see.
Thanks for all the help. Here's a few more pictures that he found from the appraisal.
-Drew
Springfield Cartridge_85.jpgSpringfield Cartridge_88.jpgSpringfield Cartridge_90.jpg