I used to own an 1861 Springfield rifle musket, and it is close to that. But it actually looks more like a combo of a few.
Look for the old Kentucky black powder muskets, or even british Enfields of that era. Zam's rifle shares characteristics of all of these.
I'm gonna go out on a limb here and say it was custom built. It's sooooo long...too long for a standard rifle.
However, if I'm proven wrong, that'll be a good thing too 
edit:::
typo