According to W.W.Greeners book,"The Gun",4th edition, published in 1888; Guns chambered for 4 bore cartridges may have bores sizes stamped as 4- 5/2- 5/1- 5- 6/2- 6/1- 6- 7/2. Whilst the measured bore size determined the the provisional proof charge.Surprisingly, the service charge is stated to be the same for all bore diameters,namely:- 9 drs powder and 3 ozs; of shot!
Refering to my earlier post in regard to the "Gates' double 4 bore; this gun has 36 inch barrels, 4 inch chambers . The weight of the gun is 17 pounds, 8 1/4 ozs.
This very fine, origional condition, gun sold in 2009 for 16,800 pounds stirling.