Mobyduck -
Congratulations on the turkey. Taking one with a flintlock should double the thrill. I got one several years ago with a William Moore 10 gauge. Alas, it was a percussion gun, but over a hundred years old nevertheless.
I appreciate your concerns with the use of Damascus barrels . I still have the same apprehensions, and I have been fooling with them for 30 or more years.
I grew up in the 30's and 40's, when every box of shotgun shells had a warning on the flap that read "Do not shoot in Damascus barrels," or something like that. As a kid, I had the idea drummed into me that Damascus barrels were inherently dangerous, and I believed it.
Today, there are a growing number of shooters who shoot low-pressure nitro loads in welded twist barrels, and the number seems to be growing. I have not gone that far, but I have shot black powder in perhaps 20 or 30 guns (or barrels) that were built in the black powder era. Each of these has been proof-tested by me before I shot them. I am so anal about this that I no longer build guns for others, just for myself. I have never had a set of welded barrels fail proof-testing, and God forbid that one shoul fail while I am holding it in front of my face.
So, I am not prepared to guarantee that anyone else's barrels will not fail. You just proof them, examine them, and, if they look solid, with no cracked welds, or rusted pinholes, make your own decision to shoot them or not. I have bead-blasted barrels to remove the rust under the ribs, and doing so really lets you see better what you are working with
Twice a year, at Friendship, Indiana, there is a gathering of muzzle-loading shooters, who compete in the NMLRA Spring and Fall Championship matches. Included are perhaps 100 or 150 shotgun shooters, who fire upwards of 100 rounds a day at clay targets. Many, if not most, of these guys are shooting antique guns with welded steel barrels. I have never heard of a barrel blowing up. Of course, these guns are immaculately cleaned and lubricated, and they shoot nothing but black powder. Also, most of these guys are not big fans of hard-kicking guns, so most of them shoot modest charges of shot and powder.
Those guns by Mike Brooks are beautiful examples of the gunmakers' art. What Mike says about the breechloader barrels flaring too much at the breech is, unfortunately, true, although I have a set of 16 gauge Elsie breech-loader barrels, which do not exhibit this swell; at least not as much as other guns do. It may have something to do with the gauge.
Moby - in response to your question about using modern steel barrels; I have done that, but they don't look as nice as the twist and Damascus barrels. Have at it, and I wish you the best of luck with your venture.
Bill