x3 pictures are critcial.
But not necessarily worth a fortune. As noted above it comes down to the variables including age; condition; completeness; and who made it (if known) - or where (if known). And any provenance!
19th Century Hawken-style rifles can go for well under or well over a grand (into the stratosphere) depending on the variables; check out the auctions, Track of the Wolf (antique firearms selection) and even the EE here, just for starters. Flayderman's Guide to Antique Firearms is another suggested reference.