I'd wonder if other experts might join in and start calling for proof of damascus barreled guns in the US just to 'settle' the issue. Thank you Demonwolf and your fellow countrymen for commenting about the realities of proof when you brought up trying to get your Trantor patent gun back in proof. That gun will still need a responsible shooter to operate it.
There are so many variables when it comes to old guns.
I do not put iron faith in proof i have two out of proof guns on ticket, an antique and the tranter patent, i have shot many more, but i fully support it at point of sale as you really can't assume the person buying has the same knowledge or understanding you have. And even then the best informed of us using our best judgement realize we are not infallible i strongly believe that individuals using these old guns understand this.
Antique guns in the collectors market in the uk are bought and sold as antiques, but if an individual wishes to enter an antique onto their certificate its assuming that if they are doing so they also have the knowledge to use it safely, many of these antiques are out of knowingly out of proof and many of them end up being entered on to certificates and legally shot.
Its not illegal to own and use an out of proof gun, just illegal to sell it.
The Lang tranters patent still poses an issue for me, i have shot it and shot reasonably well with it on some wood pigeon with black powder loads. Part of me wants to leave it out of proof and enjoy the gun. Part of me want to BP proof it just so it can be sold if i ever might need to. Part of me wants to nitro proof it, so it can be a real usable piece today and of interest mechanically.
If i do re proof in any way i will keep a record and picture the whole process of prep right through to the proof house where i will probably take it in person, if i decide to proof, i think if i do it this way even if it fails we all could learn something from it. - and then the next project can be making some new barrels!