'Jeremy' - FWIW - An original 1863 Springfield Rifled-Musket will not have a 'serial number'.

$800 would be a bargain for an original CW Arm in good 'shooting' condition.

However, use caution. There have been convincing replicas made with original looking markings.

40 years ago, Yeck Antique Arms in Michigan made a very nice Springfield copy that was hard to tell from the real thing, except it was new.

Some vendors 'defarb' Italian replicas by removing modern markings, national proofs, and correcting contours. With use, they can be very authentic looking.

A high grade replica can be worth $800. You just need to know what you're getting.

Nowadays, this means taking such an arm apart and studying threads, inletting, and parts fabrication, with a trained & experienced eye.

My $.02!