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Jack:
1st I need you to verify with a glass that the 2,579 GBP is actually 2,67 g GBP and this will give us a basis from which to begin. Also how confident are you in the 1909 - 1912 date? What is the actual diameter stamp: plug gauge or mm. Or is it plug gauge over cartridge length? Since July the 23rd of 1893, 2,67 grams of the semi-smokeless Gewehr Blättchen Pulver was used behind a steel jacketed solid projectile and sources give that the pressure was 58.8k psi. After September 1st, 1911 tubes destined for solid projectiles a 2,75 grams of powder from the Köln Rottweiler Pulverfabrik, which was also used in the Infantry Model 88, behind a solid jacketed projectile of 14,7 grams produced a pressure of 56.89k psi. But in the early 1890s the Patronen 88 was loaded with a 2,75 grams of Gewehr Blättchen Pulver 88 behind a solid steel jacketed(tombak or cupro-nickel plated)/lead core projectile of diameter 8.10mm with weight of 14,7 grams achieving a velocity of 630 m/s. About the same time, if not the at the exact time of July 23rd, 1893, the Gewehr Blättchen Pulver charge was reduced to 2,67 grams and the velocity fell to 615 m/s. If I'm not mistaken both utilized the Zdh. 88 primer. Now I'm making the assumption that Gewehr Blättchen Pulver is the same as the Blättchen Pulver Type 426 with both being used in the Patronen 88 and in the cartridges at the proofhouses. So with that, between late 1902 and mid year of 1903 the Gewehr Blättchen Pulver Type 426 was replaced by the Spandauer Pulver 682b(maybe in March of 1903) with a load of 3,2 grams behind a solid projectile diameter of 8,22mm weighing 9,8 grams and reaching a velocity of 870 m/s. Souces give the Patronen 88 reached a pressure of 3.350k atmospheres while the Spandauer Pulver 682b version only developed a chamber pressure of 3.100k atmospheres. The Spandauer Pulver 682b flakes were smaller and thinner with the sides being 1.35+/- 0.15mm and a depth of .30+/- 0.05mm while the Gewehr Blättchen Pulver Type 426 had flakes with sides of 1.7+/- 0.1mm and a depth of 0.375+/- 0.025mm. The Spandauer Pulver 682b was quicker burning as well as more consumed yielding less fouling. Now I realize I'm mixing rimmed and rimless, but with all this typed, I can't say we are any closer to answering your question but I don't think it would be for the 11,5 gram bullet but more like the 12,7 / 12,8 grams. I'd fall back on trial & error and see what the bullet spread is. Pre-1912 I wonder if the proofhouse load and regulation load were always the same? I"ll see if I can find additional info.

Kind Regards,

Raimey
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