Well, I didn't make it out. I helped my brother move some stuff, and we went squirrel hunting after. I've got tomorrow off from work, have everything loaded in the truck, so I'm fairly sure I'll try it tomorrow. About the breech plug color, the left plug is mostly brown, and the right plug is mostly blue. I can't tell what color the gun was originally. The barrel appears like it may have been brown, but most of the finish is gone leaving it mainly white. There are spots that are blue, and it appears the top rib may have been blue. The breech plugs do not look out of place when you look at the gun in hand as a whole. I've looked at the breech plug threads again, and in my mechanical-but-not-gunsmith opinion is that it is a failure of the steel. I see no evidence of gas cutting, or rust. I think it is the steel that chipped, possibly during threading, maybe not, that is for others to ponder. I also think it possible the "scars" in the left barrel were scratches that rusted. Running my fingers over them, they don't seem overly deep. Even with the possible backbore, the barrels are still surprisingly thick, far thicker than modern shotgun barrels. I should have taken a measurement.
@dave tonge, I see nothing out of place with the bottom rib. What specially are you referring to? Some of the pictures I took were as I was cleaning the gun, and was right after I took it out of the water, so keep that in mind. The breech plugs, I don't think it is unreasonable that somebody in the past had taken the plugs out to clean, and simply did not tighten them enough. I put them back in, no tape or anything else, and I'd guestimate they went in with 10 lb/ft of torque to align. I'd wish for a permanent fit, but if I built a gun with the intention of removing them, this is about how I'd want them.
I've heard a number of theory's on re proofing barrels. I'm starting to believe it is possible to do more harm, although I'm not convinced this is the case. Instead of loading it to the moon, I'm thinking I'll instead do a number of shots at a top end hunting load, say 110gr powder and 1 3/4 oz shot. If it can't handle that, then it was never safe. I'll surely be bummed if it lets go, which I do not think will happen. Even if it does, I will have something. I'll have an original I can hold in my hands when I build my own some day. It would be nice to hunt with it a while, but there is already things I like, and things I would do different.