My answer to the original question is an over-simplification in that it does not address the fact that pressure is not constant but diminishes with time and space, so it will vary with powders of different burn rates. If pressure could be kept constant in magnitude and duration (not the case with internal ballistics), a lower pressure would be required in a 12-gauge barrel than in a 20-gauge barrel to accelerate the same mass (1 ounce) to the same velocity (1150 fps).
The consideration of duration of the applied force explains how slower burning powders like Longshot produce higher velocity with lower peak pressure.
Still, I think that Pascal's law (Force = Pressure x Area) explains, at least in part, why SAAMI specifications allow higher pressure in the smaller gauges.
Disclaimer: I do not hold a degree in engineering or physics, but I did enjoy my introductory physics class, and I occasionally sleep in a Holiday Inn, although not last night.
I’m thinking I read an article on Chuck Hawk’s website, where he quoted a process engineer as stating they had changed only the primer used in a factory loading, and the pressure went up by 5000psi. What shocked me was they were altogether unconcerned about this, as long as it was under SAAMI max for the given loading.
I can probably find the article, but, when I said I usually don’t listen, that was one of many things that caused me to feel that way.
Best,
Ted
