Maximum load data differences

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LowLead

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Good evening CGN,

I am looking at several different source of load data, and noticing a lot of differences between maximum powder charges. For example, my 30.06 shoots 168 gr. Amax under 57 grains of H414. Tonight I found Hodgdon's data indicates 56.5 grains max, whereas Hornady's data says 58.3 grains should be the max. There are no pressure signs at 57.0 grains, and the rifle is grouping nicely with this load.

Other examples I've found include .338 Lapua recipes. Example, the Hodgdon and Lee data say I can put a max of 92.0 grains of H1000 under a 300 grain HPBT, but Bergers data says a max of 85.2 grains! Hornady data indicates a maximum of 89.6 grains under a 285 grain Match bullet.

I am thinking of just working up to the Hodgdon number (92.0 grains) in 0.5 grain increments, and watch for the first sign of pressure. Once there, that will be my new maximum load, then I'll work back for a ladder test.

This is similar to my 30.06 work up, but more information is always helpful!
 
"Pressure signs" appear at a given pressure based on brass or primers. It doesn't matter what the cartridge or rifles maximum pressures are. If you are looking for flattened primers that will occur around 45k psi with Federal and not until past 60k psi with CCI. If you are looking at brass, Federal brass often shows ejector marks below 60k psi and Hornady can stick in the chamber also below 60k psi. Harder brass will require higher pressures for both and some wont show "pressure signs" until well above max pressure for some cartridges while under for others. It could be 65k psi or higher which is above max pressure for both 30-06 and 338 Lapua.

Primers and brass don't know to show "pressure signs" at a given pressure based on the maximum SAAMI rating for a specific cartridge. They can be used for comparative purposes at times but shouldn't be relied on for knowing if you are over the max rated pressure or not. Short of sacrificing a rifle to a lab to do proper pressure testing, your best option is to use a chronograph and compare published velocities with what you're getting. When you hit a max rated velocity with a given powder you are most likely (but still not guaranteed) to be at max published pressure.
 
The barrel and chamber dimensions vary from gun to gun, and the powder can vary slightly from lot to lot, so naturally, the maximum loads will vary from manual to manual.
 
You will ALWAYS find discrepancies between manuals and websites. As mentioned you should start low and work towards maximum and constantly watch for pressure signs as you go.
 
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