The fact that is doesn't have a ramrod hole makes it a amateurish home built gun and not an original.
I thought I could see a ramrod hole under the barrel in the lock mortise. The gun has been made from miss matched parts by someone who didn't know what they were doing and is not the original build. I still lean toward the stock being at one time from an original 19th century gun gun.
Welding on a barrel is bad news, it creates all kinds of stress related weaknesses according to the experts at on the long rifle site. A properly mounted barrel will have dovetailed underlugs for pins or keys to hold the stock to it. I miss drilled this one and had to solder on an extension to beef it up a bit.
http://americanlongrifles.org/forum/index.php
If you can stand honesty from a guy who has done only a couple of scratch flintlock builds, I would make a wall hanger out of the gun and not waste time trying to make a functional gun out of what you have to work with.
For a certainty I can appreciate blunt honesty. But, having nothing to loose but time and knowledge to gain, im gonna play with this thing anyway.
The plan....
Grind off that nut.
Multiple heat treats to normalize barrel stresses around the welded nut.
Machine a soft steel rod to fit bore diameter and run it down the barrel.
Heat the barrel to bend the kink out so the rod slides down.
Use ball guages to determine bore diameter in damaged area. Machine the barrel to the smallest diameter that fixes the problem.
Send barrel off for hardening and tempering.
The wood stock is next. I can save it but its gonna take much work.
After redoing the wood stock, I will put it all back together and hunt with it next year.
If this doesnt work, hang it on the wall. It only cost me $10.
