Almost any "lightweight" 12-bore gun you pick up will have had the barrels struck way-down from the factory. Any 2-inch gun you measure will be no-more than .022 or .023. From what I understand, guns pass proof routinely in England now that are only in the high teens (.017 & .018). When you read the barrel information provided by Holt's on lightweight gun in their auctions you will commonly encounter this on guns with very recent proof dates.
Lloyd,
Not a Darne. Even with the ugly backbore somebody did to the gun I got from Mr. Bodio, there is a lot of .050 wall in that gun.
The 2 1/2" chamber Halifax is even heavier wall. Weight is 6lbs, 4ozs. With 27" tubes.
If you are going to deal with French proof, better bring more than .020 wall, or, be prepared to bring the barrels or action home from the proofhouse in pieces.
My understanding is a lot more old English guns are failing reproof. Lightweight, or, not.
Best,
Ted
