king, interesting marking, each pair of # indicates the bore diameter vs choke. My guess is that the gun was rechoked at the factory for some reason, maybe to meet requirements in pattern. Is there more than 1 set of proof marks on the gun? below is what the marks are in inches

left barrel
17.6 - 18.2 = .692 - .7165 = .0245 = ??
17.7 - 18.4 = .6968 - .724 = .0272 = imp mod

right barrel
17.9 - 18.2 = .7047 - .7165 = .0118 = skt-2
17.9 - 18.4 = .7047 - .724 = .0193 = mod

Jim

I learn something every day, and a lot of times it's that what I learned the day before was wrong