Proofed, proved or in this case poof. Yes I am sure of the measurement. It also is clearly stated in Holts description. The proof house does not measure wall thickness. As to how thick were the original barrels, nobody knows for certain, but I’ve been told they all started out about .020. I have a LeFever 20 which looks mint condition and it’s barrels are .020. It shows no sign of ever being reamed, honed or restruck. So thin barrels can be anywhere. Again I listed the auction item number 5855C. Look it up.

A gun is out of proof if a plug .010 larger than the plug used to determine bore diameter goes down 9” where the bore is measured. So a gun with a .720 bore is still in proof if a .730 plug will not go the full 9”. It might be .728 or .729 and if the plug won’t go it is still considered in proof. Also any alteration of chambers will put it out of proof. So if the barrels start out at .025 thickness and gets cleaned up to .008 to remove pits it still is in proof. But and this is a big, but the wall thickness may have gone from .025 down to .017. Thin but still in proof. You will see this commonly listed as “barrel below recommend thickness”. It is still in proof and legal to sell. Deciding if you want to shoot it requires you to measure it accurately and then make a judgement. But never assume just because a gun is in proof it is always safe.