Black-Hog-Down said:
I'm talking about +p or maybe a little higher.
Since "a little higher" is outside the SAAMI limits, it's what the commercial makers call +P+. There is no upper limit on +P+, because, by definition, it's outside SAAMI limits. It is going to be outside published loads, and hence the warning added to the original post, even if it's only by a little bit extra.
Now the dirty little secret that may cheer you up. SAAMI specs are for manufacturers insuring compatibility in all weapons of the same chambering. Most people don't understand how the SAAMI standards work and handloading manuals don't typically use the SAAMI numbers the way manufacturers do:
they load lower.
Here's part of how the SAAMI statistical method is used:
The maximum pressure number we commonly see is called the Maximum Average Pressure, or MAP. This is the highest 10-shot peak pressure average a random sample of 10 freshly loaded rounds produces, fired in a minimum size chamber with the powder back over the flash hole (highest pressure for position-sensitive loads). But it is a maximum for the
average and not the maximum for individual rounds that contributed to that average. Those individual rounds go both above and below the average to result in that average.
The actual highest individual cartridge pressure is determined by another number called the Maximum Extreme Variation (MEV), which limits extreme spread of peak pressure among the ten rounds in the test sample to about 18% above the MAP in the worst possible case. That case is rarely, if ever, seen, and a more reasonable expectation is the highest individual peak pressure will fall within the limit used by the European CIP, which is 15% above MAP.
Handloading data manuals don't use the MAP as an average. They use it as an absolute limit. If you look at the maximum loads in Hodgdon's data, for example, their pressure listed is below MAP and isn't the same among different powders. That's because they take the variation into account and adjust the maximum load so the highest pressure value the record for an individual cartridge never exceeds the MAP number. This approach is spelled out in Hodgdon's printed manual, where they advise you that the highest maximum load pressure you see among various powders is highest because that powder gave them the least variation and is therefore the most consistent.
There are reasons the manual creators do this. The main one is that they know each lot of powder will vary in burn rate from others and that you are using fixed load recipe's not based on the individual lot number you purchase, and that you rely on it to be safe rather than rely on a pressure test gun to determine your load. A commercial loader has the pressure gun, so he can use it to adjust charge weight to compensate for powder lot variation, but most handloaders cannot do that. Another factor is just erring on the safe side for liability reasons.
So, the bottom line is that published loads may be as much as about 15% below true maximum values. On the other hand, I have three times now run into published minimum starting loads that were already at maximum for the individual gun involved. So you want to start all your load work ups with the lowest load listed, but not be surprised if you can go beyond maximum in some cases, watching carefully for pressure signs. So be conservative and stay safe.
rg1 said:
I've always read that +P loading should be only done with NEW brass and not multifired cases and fired +P cases should not be reloaded again at +P levels.
Actually, that is not a valid generalization. An example: The .38 Special has a MAP of 17,000 psi, and the +P has a MAP of 20,000 psi. Yet, Elmer Keith used the .38 Special case to develop the .357 Magnum cartridge, which has a MAP of 35,000 psi and he successfully reloaded those cases many times and you can reload a .357 headstamp case multiple times, even though most manufacturers give it the same head they give a .38 Special.
You just have to watch your cases and primers for expansion. No way around it.
