doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com 20 gauge English nitro proof question

Good morning! I have read as many threads as I can find regarding 12 gauge proof pressures, and the various psi/ton/bar conversions and such. I'm tolerably familiar with them, but i just saw a 20 ga for sale with nitro reproofs (rifle conversion). What did the gents across the pond normally proof 20 gauges to? Is it the same 3 or 3.25 tons that 12's were? Unfortunately I dont have any pics of the proofs to see

1925-1954 the 20g 2 1/2" would be marked "7/8 oz." for a service load of 2 1/2 Dr. Eq. = 1210 fps at 3 Tons (but not marked as such). 20g was frequently loaded with 2 1/4 Dr. Eq. as in the U.S. however.

After 1954, 2 1/2" 20g (still 7/8 oz.) were usually 3 Tons;
2 3/4" 20g were 3 1/4 Tons.

The 1954 Rules of Proof �Highest Mean Service Pressure� equivalent transducer values as converted from LUP by Burrard�s formula:
3 tons = 8,960 psi
3 1/4 tons = 9,800 psi

The 1969 Commission Internationale Permanente pour l'Epreuve des Armes � Feu Portatives standards were not ratified by Great Britain until 1980
http://www.cip-bobp.org/homologation/en/tdcc_public?page=1&cartridge_type_id=7
Both 65 and 70 mm 20g standard is SERVICE 830 BAR or 12,038 psi;
MSIP 950 BAR or 13,779 psi;
PROOF 1040 BAR or 15,084 psi.

20g service pressures under the 1896 Rules of Proof
https://books.google.com/books?id=inQCAAAAYAAJ&pg=PA296&dq
Pressures were measured using crushers (LUP) and reported in pounds/ sq. inch; modern piezoelectric transducer pressures would be 10 - 14% higher.
20 bore Service charge = 7/8 oz. 2 1/2 Dr. Eq. (1210 fps) = 34 gr. Bulk Nitro powder
C&H �T.S.� No. 4 BP - 8,240 psi;
�Schultze� - 8,220 psi;
�E.C.� - 9,100 psi

Frederick Toms, Sporting Guns and Gunpowder, 1897
https://books.google.com/books?id=inQCAAAAYAAJ&pg=PA132
Average pressure of Nitro powders
20g 7/8 oz. 3 Dr. Eq. � 3.56 Tons = 10,840 psi
https://books.google.com/books?id=inQCAAAAYAAJ&pg=PA158
20g 2 1/2 Dr. Eq. and 1 oz. � 3.07 = 9,195 psi

https://books.google.com/books?id=inQCAAAAYAAJ&pg=PA325
20g with 7/8 oz.
35 gr. Bulk (2 1/2 Dr. Eq.) � 2.39 = 6,910 psi
22 gr. Dense � 2.93 = 8,725 psi

�The Long 20 Bore Cartridge�, The Field in Forest & Stream, October 17, 1908
https://books.google.com/books?id=ejQevDPMUIYC&pg=PA630
2 3/4� case with �Schultze� Bulk Smokeless (42 gr = 3 Dr. Eq.)
The standard 2 1/2� case was loaded with 33 gr. �Schultze� = 2.36 Dr. Eq. (about 2 3/8) with 13/16 oz. shot.
36 gr. = 2.57 Dr. Eq. with 15/16 oz. = 4.65 tons = 14,504 psi (using Burrard�s formula)
37 gr. = 2.64 Dr. Eq. with 7/8 oz. = 4.54 tons = 14,134 psi
35 gr. = 2.5 Dr. Eq. with 13/16 oz. = 3.45 tons = 10,472 psi

William Bruette, Guncraft: Guns, Ammunition, Wing & Trap Shooting, 1912
https://books.google.com/books?id=5g51K93as84C&pg=PA210&dq
20g 2 1/2� case 33 gr. Curtis & Harvey's Amberite Bulk Smokeless (2 1/3 Dram) 13/16 oz. = 11,648 psi