400m When I purchased te gun the dealer told me it had no issues with the barrelas, and I asked. Now I can hear you laughing but this is a well known dealer and I would trust him. Like I said, I had several dealers look at the gun at the Southern Side by Side shoot and they all inspected the gun from one end to the other. I will name a few again for your viewing pleasure, Atkin Grant and Lang, William Larkin and Moore, Vintage Doubles. If there had been an issue or some doubt I think they would have brought it up. In fact all were willing to take in in trade. So why would they take a pig in a poke if there was any questions?
Now I do not claim to be the most knowledgeable person about "proof". If you can tell me how to tell if it is then I will look and let you guys know.
All I know is the gun has been gone over a lot in the last couple of months and wall thickness was checked and re-checked and no problems were found.

Mike Proctor