Good points, Roy. However, my main point remains valid: Chamber length would have been marked on a gun from the 1925-54 period, and in fact the presence or absence of chamber length is the easiest way to date a gun as being either from that period or from 1904-25.
Also, what's your source for maximum breech pressure for guns of that era? And if you're quoting psi figures from the days when pressure was measured with lead crushers, you have to remember that the figure you're giving is what we'd call LUP today, not psi. (Unfortunately for mutual comprehension of pressure readings, the British continued to use lead crusher measurements rather than piezo-electronic until just a few years ago.)
