Max Loads - not max pressure

was looking over some data in books. bear with me, since I'm new to reloading and hoping I can get some better understanding of this. It seems to be fairly common for max loads to be listed, and sometimes they also include the pressure at that load. often times, the pressure is way below the max for that cartridge.

that being said - I get for lead bullets, like for .357 - the max load will be based on an appropriate velocity to get good functioning, so - it is nowhere near max pressure for the cartridge.

are there other scenarios where a max load would be below max pressure? unless I'm remembering wrong - think I was looking at some that were for jacketed, that were also well below max pressure, just curious what the limiting factor there might be - to have that be a max load.

nope - was just me looking at the tables to quickly, and not realizing I was looking at CUP and not PSI ..

Bfh_auto said:

A lot of tested data stops when there are unacceptable pressure swings with the same powder charges.
Some powders peak very quickly, so there is less room for error. This must be calculated for to keep us safe because we don't have testing equipment.
Hornady is noted for doing this. I also find my most accurate load is always somewhere inside their somewhat conservative data.

Click to expand...

that is very interesting. I was looking at load data - and there was one that showed incremental powder increases, velocity, and pressure. the max load was only 45fps more than a lower charge that had 25% less powder, and 2,500psi pressure difference. I don't recall the exact data I was looking at, but it made me think the gains of loading up aren't linear to the risk of the pressure curve if there was a small mistake or variation in the load/cartridges.

been looking, but haven't found a definition of Maximum Average Pressure. Well, I have - but not one that actually explains what they are averaging, so - to say "max average pressure = max average pressure" is not actually a definition of anything, but that is what they seem to always put.

I can assume what it means, but that seems like a bad idea - but, really not able to find a definition of what the average is of when calculating this - it could mean 2 things from a science perspective, maybe more

1. The average pressure maximum applied to the chamber surface area when firing a round. Thus the average is of pressure applied over a surface area at a moment in time - when the pressure is at a highest peak. 20,000 psi is the average max pressure over the chamber area surfaces at peak pressure; average of pressure over a surface area at a moment in time.

2. The average pressure, over the time there is pressure in the chamber and barrel. So the average would be over a period of time. 20,000 is the max pressure in the chamber over the duration of time it takes for the round to exit the barrel. In theory anyway - I'd think this method would result in a much higher peak maximum pressure, and vary significantly depending on barrel length etc.

So, what are they averaging? - is the Max Average Pressure the average pressure at peak over a surface area in a moment in time? or is it something else like example 2 shown above? or something else?

Interesting. So, it is an average from some number of sample fired rounds and the maximum pressure reading of each round averaged to calculate MAP.

then they use that MAP, to calculate proof loads … starting to get a better picture of this.
https://en.wikipedia.org/wiki/Proof_test