Originally Posted by Drew Hause
Probably the best data as to loads and pressures of British shells under the 1925 and 1954 Rules comes from Major Sir Gerald Burrard, The Modern Shotgun, 1955, 3rd Revised Edition Pressures converted to transducer psi from Long Tons/ Sq. Inch at 1”
12g 2 1/2” 33 gr. Nobel Smokeless (3 Dr. Eq.) with 1 1/16 oz. - 7,885 psi
12g 2 1/2” 33 gr. C&H Smokeless Diamond (3 Dr. Eq.) with 1 1/16 oz. - 8,288 psi
12g 2 1/2” 31 gr. Smokeless Diamond (2.8 Dr. Eq.) with 1 1/16 oz. - 7,179 psi

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I still find it curious that proof pressures seem to be related only to gauge and chamber length. A gun made by the same shop, with 2.5" chambers cannot handle the service pressure of another from the same shop made with 2.75" chambers and identical lock-ups. Yet two guns made in different shops, much different in construction including locking lugs and barrel materials and thicknesses are proofed to the same pressures, if they have the same chambers.

I have never seen a good justification for this.

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BrentD, (Professor - just for Stan)
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