The practice of lengthening the chambers of English guns from 2 1/2 to 2 3/4 accompishes only one thing,It rendered the gun out of proof!
The practice of lengthen chambers dates back to the time when a 2 3/4 shell actually measured 2 3/4, These old shells had card tubes and a rolled turnover.The card tube had a wall thickness greater than todays plastic shells which also possed an increased safety risk if an atempt was made to load them and shoot them in in a 2 1/2 chambered gun!
In reality it was all but impossible to close the action of a 2 1/2 chambered gun with a shell that actually measured 2 3/4 !
It was this issue that prompted ill informed owners to demand that their gunsmiths extend the chamber length of their guns to make them useable!!
The closed length of todays 2 3/4 plastic shells is approximately 2 1/4 inches,after firing it measures approximately 2 5/8 inches.bearing in mind the thin wall of plastic shells and the pressence of a forcing cone from chamber to barrel bore there is virtually no constriction on discharge. I believe it was Burrard that said , "No cartrige case ever caused a barrel failure."
It is the pressure ceated by the weight of the charge &wads in combination with the explosive force of the charge including the the cap, that creates the pressure in the gun barrel
English guns with 2 1/2 inchambers are proof tested at a lower presuure than guns with a 2 3/4 chambers
Those considering extending the length of 2 1/2 chambered gun to 2 3/4 inches ,should ask themseves, Dose removing metal from the barrels of my gun increase their strength or dose reduce the factor of safety?
In 60 years of gun collecting i have seen 100;s of Fine guns put out of proof and in some instances ruined by chamber butchery.
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