I thought about this thread for awhile before offering this commentary to the group.

I have 2 out of proof guns. There is a distinction about out of proof.
1.) Out of Proof cannot be sold. However, if I choose to have a barrel opened greater than .008 and intend to keep the gun, it doesn't require reproof. The gun is not changing hands/being sold. I had an Edward Lang under-lever Damascus hammer gun modified. It was cyl/full. The left barrel was already too big.
I had the right barrel reamed to leave 0.010 of choke at the end.
I had the left barrel choke opened from .040 to .020.
Now I have a IC/Mod 30" hammer gun by one of the Lang brothers with decent chokes.
My MWTs are .036/.028. (A long way from 9"). The chambers are still 2 1/2".
The original bores were 13 (.710). They are now .738/.738
Yes, if I intended to sell the gun, I would have reproofed it.
But, I am not selling it, so it was not required.
I chose not to subject the Lang to modern proofs.

2.) An out of proof cannot be sold. I have a really pretty Army and Navy SLNE 12. Something along the way damaged (buldge?) the left barrel 16" from breach. The external damage was struck down and the bore honed to remove any evidence.
When they were finished butchering, the BWT was .011 16" from the breach and the left bore had opened to .743 (from .719). The thinness was right where your hand grabs the barrels prior to shooting. I have a barrel wall thickness gauge with 16" sticks. The damage/thinness is right at the limit of where my rods reach. It could have easily been missed. Many folks have barrel wall gauges with 10" rods, since proof thickness is measured at 9". Baloney, I care about my hands.
The gun was never sent to proof. It was given away with the condition it never be sold or shot.
As President of the Carolina Vintagers, I now have the gun and use it as a training tool (firing pins removed).
The gun looks great. The economics don't support a sleeving for a SLNE.
So, it will spend it's time with me showing SxS fans WHY IT IS IMPORTANT TO MEASURE BARRELS.

Joe Norcom