tinker - if you ever get an answer for your question, I'd sure like to hear it!
Like you, I've picked up old barrels over the years. Several I have bored out to smoothbore. I bought them when I could get them cheap - 2 to 10 dollars - then all of a sudden, they became valuable? Give me a break. Unless, like the one fella said, it is an original Hawkin barrel or something like that - it is just what you describe it as - a rusted piece of iron. Yes, they can be bored out, re-rifled or a rifled liner put in - but, if it is rusted and pitted badly, is it really worth anything? I guess it is up to the person that wants it for whatever reason. I had accumulated a number of them and finally sold most of them on eBay about 5 years ago - to my amazement, they brought decent money and I made some good profit off of them. I have a couple left and will probably do what you are talking about - cut them down, bore them out and either leave them smoothbore or put a rifled liner in them. But, my time and materials are worth something so am I going to save $ doing it over just buying a new made barrel - probably not. Most of these barrels you run across are left over from guns that were parted out or they are the sole survivor of what was once a firearm. I don't find a great quantity of original muzzleloaders that are missing just the barrel and if you did, you might hunt a long time to find a barrel that would fit in the channel and work proportion wise. So go figure . . . . You do have a nice tapered barrel there that with some MAJOR re-work, could be a good barrel - but again, a lot of hours, work and sweat. The majority of truly old, original barrels have breechplugs with very coarse threads - oftentimes rusted, pitted, etc. and it can require a lot of machining and possibly cutting off the breech and re-breeching with a new breechplug (if there is enough barrel wall thickness to do it). I half imagine that a lot of people who view these old barrels as "valuable antiques", buy 'em and take them home and they end up collecting dust somewhere. I once had an original 1816 musket barrel that had been reworked at an arsenal - rifled, rebreeched to percussion and a long range sight installed. It had been through a fire and was heat warped in two places. I sold the long range sight separately and at a gun show, sold the barrel to a guy who went bananas over it - he was going to build a musket around the barrel to shoot NSSA. For a wall-hanger, it would have worked O.K. - but, to attempt to use it as a shooter? I tried to discourage him but he knew more about it than anybody else. When he finally asked me what I wanted for it, I threw out a price of what a mint original barrel just like it would go for. I thought he'd turn on his heels and walk away - he didn't - he shelled out the cash for it and thought he had something nobody else did. I pointed out everything that was wrong with it, took the breechplug out and let him look down the barrel and see the obvious warps and it still did nothing to prevent him from wanting it. I finally just figured that the customer is always right and sold it to him. I used to shoot NSSA but I never heard of an event for muskets that would shoot around corners. I often wondered if he got his "dream gun" built around it or if it is serving somewhere as a fence post for which it was better suited.
Good luck with your barrel and whatever you do with it, I hope you'll let us know how it worked out! Thanks! bedbug