Proof . . . although wall thickness is a critical measurement, there is no set standard that automatically renders a gun out of proof due to thin walls. Think I do recall reading that the proof house wouldn't accept guns with something less than .018, and the British gun trade recommends thicker walls than that. But personally, I'd shy away from a 2 1/2" gun with MWT under .025, probably .030 if it's 2 3/4".
What you can spot from the barrel flats, and with bore and chamber gauges, is whether the gun is out of proof due to lengthened chambers (which may or may not be a problem as far as the gun being a "shooter" goes) or the bore being more than .010" over the standard for that particular gauge--but that really isn't a problem either, as long as there's sufficient wall thickness, even though it does automatically render the gun out of proof.
Agree with most of the posters above. I've shot several Brit game guns a lot on targets, using 7/8 oz reloads in 2 3/4" hulls, loaded well within appropriate pressure standards. Not any more problems with the Brit guns than with European or American guns of similar vintage.
