I had Toby restore an Edward Lang hammer gun for me. I knew the left barrel was honed beyond 8 thou (out of proof), when we started. It needs reproof prior to sale.
Here is the thing. I wasn't going to sell it. I didn't want to risk my gun at the proof house. My barrels are plenty thick (+32 thou). It is still out of proof in the left barrel. I bought it with a big dent in the left barrel. I raised the dent. I then used it to practice browning. It came out great. So, I shot it. It shoots great. It needed the left firing pin sorted out as the nipple was prone to fall out. (puns expected)
I now have a 30" E. Lang hammer gun with IC/Mod chokes. It is a a great gun.
At my request, Toby did not submit the gun for reproof. This was my choice as the owner.
I would never offer this gun for sale in the US without the disclaimer that it is out of proof. It's a keeper.
Joe