Wow! I was away from the computer this weekend and am amazed at the great response.
You all may be familiar with this book already, but I found an incredible resource yesterday at a local antique shop-Modern Gunsmithing by Clyde Baker c 1933. Was up half the night reading it. He mentions the insertion of tight-fitting cotton to plug the void pressed about an inch in from the muzzle, then pouring zinc chloride into the hole and then decanting it out. Next, soft solder is melted and poured into the hole to fill and filed off. Same idea as the steel wool, but not sure where the Zn comes into play. Also, I'm not sure how widely this book was read, but Mr Baker may be to blame for the the hinge pin peening to bring guns back on face as he does advocate this for the "working man's" American double. Other than this though, sound advice and some neat period info including some chapters by Townsend Whelen, the developer of the 220 Swift I think.
BTW, I also picked up a copy of our own Steven Dodd Hughes' book on custom doubles (not at the antique shop). Great info as well--and interesting to read about how the grainy black blue rust finish was achieved on the Fox. Beautiful guns, too!
I haven't had a chance to do anything yet, but as I'm so close to Earlysville myself, if Prof Apperson is willing, I'd like to bring the gun to him (and also an orig Parker 28 I found to show off).
Thanks so much,
Bill