Yesterday's Weapons Forums

Awhile back I was looking into proof pressures of other rifles and remembered having read somewhere that at least one proof house had tested both the .303 Lee Enfields and the 8mm Gew 1888 at the same pressure levels, 58,000 PSI.
Well I haven't found the original source for that information but I did find out more on the Gew1888 Proof test pressures, and these appear to be in true PSI rather than in CUP, though arrived at by the same sort of pressure guns.

The Gew 88 proof load used a then new system of measurement, the pressure of the proof load was expressed in Metric atmospheres, equivalent to the more recent British practice of expressing pressures in BAR. Both use the average atmospheric pressure at sea level as the base.
The Gew 88 proof load was rated at 4,000 metric atmospheres, which this source (5th Edition Gun Digest Treasury) gives as 58,800 PSI. How close these figures are to true PSI is impossible to say.

The earlier source I mentioned, which I haven't found yet, gave 58,000 PSI as the proof loading of the .303 and rifles chambered for the 8mm J bore cartridge, and gave 78,000 PSI as the proof pressure for WW1 era Mausers.

The Gew 1888 proofed by the above method would bear a mark as follows. '2.67 g. GBP' over the mark 'ST. M.G.' the latter stands for the type of service projectile "Stahl Mantle Geschoss" (Steel jacketed). 2.67 g. is the powder charge in grams of the special powder " Gewehr Blattchen ( Rifle Flake) Powder" used only for proof loads and not available to the public, and not used for any other type of cartridge other than proof test cartridges.

Other markings you may find are 8 mm over 57 and St. M.G. over 14.7 the last being the standard bullet weight in grams.

Other bullet designations you might find on sporting rifles are K.M.G. "Kupfer Mantle Geschoss" ( copper jacketed) and "Bl.g" which stands for Lead bullets.