Influenced heavily by the very logical reasoning and findings of my mentor the late Homer S Powley, I've learned that a working peak pressure of 45,000 to 47,500 copper units is about the best, all around, for cartridges that SAAMI used to rate at 50,000 to 55,000 copper units. SAAMI now rates these cartridges at 60,000 to 65,000 lb/sq in.
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<br>There's no rigid relationship between copper units and lb/sq in., of course, so we can only approximate what this pressure is, in lb/sq in. A good approximation is about 50,000 to 55,000 lb/sq in. -- an approximation, not an exact equivalent in different units.
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<br>At these pressure levels, muzzle velocities increase and decrease very little with significant increases and decreases in pressure -- so there's little gain with higher pressures, little loss with lower pressures. And the differences in trajectory, impact energy, penetration, and expansion are too slight to discern in the real world.
