Drew,
I am not surprised by the results posted. What appears to be overlooked in tests of this type is the importance of recording the expanded length of the shell and the wall thickness of the shell casing.
A modern day 2 3/4 plastic shell case when fired/ expanded measures 2 5/8,inches approximately thus entering a 2 1/2 chambered guns forcing cone by approximately 1/8 of an inch. A typical plastic shell case wall is .025 thick. If we consider that the Diameter of the chamber at the mouth of the forcing cone on a 12G is .800 approximately a 1/8 protrusion into the forcing cone dose not create a reduction in diameter that is likely influence breech pressure. As seen from the test results the recorded breech pressure varies from the combination of powder plus cap, plus charge of shot and weight of wad in the test charge.
It was a much different scenario in the 1870-1900's when a 2 3/4 shell measured exactly that and shell cases used a card tube which was thicker than todays plastic. The net result was bore restriction if chambered in a 2 1/2 chambered gun.[ie always assuming you had the strength to close the action!]
The key safety issue in so far as, "In proof" English guns is concerned is to is to make sure the shells used do not exceed the approved breech pressure. I think it was Burrard writing on this subject who said," no shell case ever burst a gun."
Last edited by Roy Hebbes; 04/13/15 09:38 PM.
