A few points I think worth mentioning. The "Standard" shot load for a 2½" chambered British gun was 1 1/8oz prior to WWI. To conserve lead it became mandatory for the makers to only load 1 1/16oz during this period. British ballistics of the era primarily listed the "Observed Velocity" which was the average over the first 20yds of flight. Conversion tables for these loads show many were much closer to 1300fps MV than 1200fps.
The 12/C in a diamond indicates any chamber "Shorter" than 3", thus an original 2 3/4" chamber of that era is also marked with 12/C in a diamond. After the standard shot charge wt began to be marked then that will help define the original chamber length ie 1 1/8 for 2½" chamber; 1¼ for 2 3/4" etc. As I recall I believe that actual chamber length & "Tons" pressure came in at about the same time. Prior to the shot wt marking there was really nothing in the proof marks to determine chamber length.
As a side note the standard USA ballistics quoting a 3DE-1 1/8oz load as 1200 fps MV was almost univesally applied as velocity over the first 15 ft for many many years. After the charge leaves the muzzle it seperates quickly so that individual drag replaces the drag on the charge as a unit. Velocity falls extremely rapidly at speeds in excess of the speed of sound. That 1200 fps is quite a bit "OFF" of true MV or the velocity at exact exit of the muzzle.
PS; that 1/31 should read 13/1 which denotes a dia which will accept a .719" dia gage but not a .729" one to a depth of 9" down the bore from the breech.
Joe; you posted some of this while I was writing. I should have added longer chambers were marked 12/LC (long chamber). The wording on this is just a little ambigous however & is not entirely clear if this mark began with 3" or for anything longer than 3".
Last edited by 2-piper; 01/27/10 01:47 PM.
