Hi guys,

I've been paying more attention lately to stated pressures in reloading manuals. The part I don't understand is that a given load in my 338 federal shows a max charge of a given powder and a pressure of say 52000 psi.

Further down the chart using a different powder the velocity may be the same or lower but a pressure of 61000 psi.

If the operation pressures can go as high as 61000 psi, then why can't the manufacturer of the powder raise the charge until 61000 psi is reached or loaded to compression? Would this not give you max velocity with that powder along with max pressure?

If someone could clarify this for me it would be appreciated.

Thanks,
Mike

Pressure isn`t fixed when a cartridge fires. The pressure will cover a range the same as your velocities do when cronographed and the listed pressure in the book is the average. If you look at the graph I`ve posted you will see there is a 5K+ swing in the pressures recorded. The average was 48+ K and the max was 52+ K. Don`t take this a being a true PSI listing, I use it as a Pressure UNIT record.


There are acually two SAAMI max pressures, the Max average pressure and the MAX PEAK ALLOWED pressure. Your 61000 psi max listed in the manual is likely not giving as wide a pressure swing and they can get a average that is higher without going over the max allowed. The labs will work up a load with a average that doesn`t excede this while staying under the "max allowed" pressure. The 338 Win mag has a SAAMI max average of64,000 psi with a "max allowed" of 65,000 psi according to the A-Square manual. The powder giving you a pressure rated as 52K "average" in your book is likely showing pressures at or exceding the 65K "max allowed" when the lab tried to raise the charge higher. The 61K load is probably much more consistant, and able to be run at a higher psi without exceding the "max allowed"

Generally the highest velocity without exceeding max pressure is with a powder that fills the case and just reaches max pressure.

Powder that are slower cannot fit a charge that will get max pressure, and so have lower velocities.

Powders that are faster will have less than a case full, max pressure, and lower velocities.

The velocity is the result of the area under the pressure curve, and slow powders have too low a pressure. Fast powders have a quick peak with little duration of pressure. The best powder gets it up and keeps it up.

The maximum pressure for an 1892 7mm Mauser case head [338 Federal, 300 Savage, 30-06 etc.] is ~ 62 kpsi commercial sales and ~ 65 kpsi handload for a specific rifle.

Advanced hand loaders learn to read the indicators of short brass life, find the limit, and back off the charge by a safety margin of a few %.

In 1956, Vernon Speer was saying that safety margin was 6%, but if you back off 6% you will be below 61 kpsi.