OK, that makes a lot of sense. When you refer to two Skeet's gauges are you talking about ones for different bores?

The one inch micrometer (I think I have a small one too that my Uncle gave me in 1953)and the skeet's gauge would give you the average thickness of the barrel since you are subtracting the ID from the OD. Is that the idea?

Easy to carry, just need to bring my super spectacles.

So many guns, so little time!