For a cartridge that’s so well documented, the .276 Pedersen is a bit of a puzzle to me. This milsurps.com article gives the peak pressure of the cartridge as 19 long tons per square inch, or 42,560 PSI. This is quite low, lower even than 7.62x39.

Hatcher’s Notebook gives the velocity of the .276 Pedersen at 78 feet as 2,690 ft/s, which works out to 2,740 ft/s muzzle velocity.

Using CAD software and this cartridge diagram, I modeled the case volume of the cartridge, which resulted in 47.4 grains case capacity. Weighing one of my pulled bullets, I got a bullet weight of around 126 grains.

I plugged the dimensions of the cartridge, the bullet weight, and barrel length of 24" into an online Powley computer to see if I could replicate the original performance. I was unable to reach the velocity stated in Hatcher’s Notebook without reaching a pressure of at least 53,000 PSI. The pressure stated in the milsurps.com article gives a muzzle velocity scarcely higher than 2,500 ft/s, far short of Hatcher’s value.

So what’s going on here? Does anyone have any insights?