I think the proofing of a century ago in comparsion to that of today would likely be looked upon as "Shade Tree" by many. At that point in time I think no "Careful Measurements" were made before & after firing. Reading Greener on Modus Operandi of proofing he describes how a rack of plugs is used & the bbl stamped according to the largest which would enter the requisite distance, the loader then charged the bbl according to the stamped number. After firing then it seems the "View" mark meant basically what it said. A man with an "Experienced Eye" which is able to detect extremely small bulges examined the bbls & if found good stamped the proof mark upon them. If a bulge was present it was not stamped but returned to maker, who according to Greener would normally hammer the bulge down & re-submit & the bbl would normally pass on the 2nd firing. Seems the cold working increased it's resistance to bulging somewhat. I think the proof house did not determine a bore was say .721" & then stamp it 13/1 but simply the 13/1 (.719") plug would enter & the 12 (.729") plug would not. Bore was somewhere between those diameters. If a visable bulge was detected the bbl was rejected.
