Interesting. It's certainly true that under both SAAMI (US) and CIP (European) standards, the maximum average pressure (MAP) for 12ga is lower than the 20ga MAP. But looking at the Alliant Powder website and comparing 1 oz loads, I can find a 12ga load with a peak pressure of 10,870 psi and a 20ga load with a peak pressure of 10,300 psi. Depends on the components used in both loads.
How does one go about determining the total pressure for a given load? When comparing MAP, while the 12ga standard is lower than the 20ga, the difference--SAAMI 12ga MAP vs 20ga--is only 500 psi (11,500 vs 12,000). That's nowhere near 40%.
Larry; First & Foremost that 11,500 vs 12,000 is Max Peak Pressure "NOT" Max Average Pressure. Average pressure will be way lower than the Peak.
Nope. I'm quoting straight off the SAAMI Voluntary Performance Standards, Miller. Max Avg Pressure for 12's is 11,500; Max Probable Lot Mean is 12,000; Max Probable Sample Mean is 12,800. For 20ga, either 2 3/4" or 3", the figures are 12,000; 12,600; and 13,500.
