Bugger,
Thanks for your definition. Just wanted to know, because when SAAMI lists +P loads they define it with a specific maximum average pressure (MAP) for that cartridge. For instance, the only rifle cartridge I can recall offhand with a SAAMI +P pressure level is the .257 Roberts, and the +P pressure is 58,000 PSI--which is less than the .30-06 standard of 60,000.
SAAMI lists the maximum average pressure for the .270 at 65,000 PSI, which is also the top MAP they list for any cartridge. There are several reasons for SAAMI to list a MAP for certain rifle cartridges under 65,000 PSI, such as erratic pressure spreads (the reason the .243 Winchester is one example) and weak brass, but the .30-06 has never shown either tendency. Instead the MAP is 60,000 because of so many old .30-06's.
I don't see any reason not to handload the .30-06 to higher pressures in a modern rifle, but the question is how's +P pressure determined?
Probably the best method for the handloader is velocity, since measuring case head expansion has so many problems it's actually pretty useless. According to one old rule of interior ballistics, when using single-based powders pressure increases at approximately twice the rate of velocity.
Another (and more precise) rule is that velocity with single-based powders increase at the same rate as the powder charge: If the powder charge increases 1%, then velocity increases 1%.
Combine both rules and the increase in presssure from 60,000 to 65,000 PSI is 8.33%. But since velocity will only increase half as much (again, with single-based powders), then the increase will be about 4.16%. In a 180-grain load at the standard 2700 fps this means an increase to 65,000 PSI will result in about 2810 fps. However, some powders already reach about that level even without increasing pressures to 65,000.
But as far as an article about such increases, well, it presents all sorts of problems, including accurate pressure-testing when working up loads--and then persuading some magazine or website to publish the results of handloads exceeding standard SAAMI pressures.
Back in Bob Hagel's day this wasn't a problem, the reason some of his .30-06 handloads reached very impressive velocities--which I am sure required pressures over 65,000 PSI. But it is today, for better or worse.
