British proof rules match the bore sizes given in Daryl,s chart.
4 bore barrels according to Burrard are normally bored at 6/1[.938 diameter]but in actual fact the bore size of a gun deemed in proof as a 4 bore can vary in diameter from 1.026 to .919. The provisional proof load varies depending upon bore size. The definitive proof load is the same for all barrel diameters and is also the same for both 4.0 & 4 I/4, chamber lengths.
It was the gun makers responsibility to make sure that barrel wall thickness was sufficient to with stand proof at the intended final bore diameter.
Last edited by Roy Hebbes; 05/25/13 07:05 PM.