Load single shells increasing in 0.3 grain increments until your primers look like this:
Or your bolt lift becomes stiff.
Now you know your rifles pressure maximum.
Photo credit to yomomma
Excessive headspace can create the same case/primer result and NOT be a cause of pressure so...
Quick thoughts and you can refer to SAAMI and reloading manuals for more data. There will be CUP rating but that gets confusing so will just stay with PSI which most understand. ALL SAAMI registered chamberings have a max pressure rating. They are no where near the same for a whole host of reasons. CIP (European regulating body) can have a different pressure rating for the "same" chambering.
Standard pressures typically top out at 56,000psi. The 308 Winchester is one of these standard chamberings. This group has the widest range of pressures as it covers the vast majority of chamberings from the beginning of smokeless powder to today. This is not a universal rating as you will see by looking at any reloading manual that lists pressures for with their powder data. It is truly all over the map and yes, you can find many contradictions depending on firearm and era of data.
Magnum pressures typically top out at 65,000psi. As these are affecting post WWII chamberings for the most part, there is more consistency in the pressure ratings with any chambering considered "magnum" BUT there are most certainly exceptions like the 375 H&H 'magnum" which is actually loaded to very low max pressures.
Proof pressures. These are used to test actions and rifles to ensure they will handle an overpressure situation without risk to end user.... ie the kaboom that doesn't cause the gun to come apart. This is not an operating pressure but a test to ensure product safety. Typically ranging up to 80,000psi... the test ammo is heavily regulated, certified and typically sourced from a specific lab. Many factory rifles get a couple of these rds before leaving the factory.... so yes, they pop out of most current factory rifle without muss or fuss. I have a couple of these cases and there is no outward appearance of pressure.
Many modern components ie brass, primers and powders, are designed to work and usually thrive at magnum pressure levels. Pretty much all LR competition shooting is in this range of pressure so yes, competitors are going beyond book loading when loading standard pressure chamberings like the 308W. Most will find best accuracy in the magnum pressure arena which is in the 60/62,000psi range. With careful set up, work up and testing, many competitors reap the benefits of better performance AND accuracy when going to what is essentially +P loading.
Problem lies in components that are "overly" strong and vault tight actions that do not give expected pressure signs even at elevated pressures. Here shooters can assume they are safe and have some amazing results... but there is no free lunch. Just because you do not see pressure, it is there. The only real way to know is to put a pressure trace on the set up and test in real time... velocity is useful but definitely not the end all wrt to confirming the actual pressure in the pipe.
But if the speeds of a set up vastly exceeds what is considered typical, safe assumption pressures are way off side... no magic formulas in the world of civilian reloading... there are millions of dollars in research trying to find it. The stuff we find on a shelf is not part of this "good stuff".
Personally, I feel components that do not show pressure signs past magnum pressures should be banned for safety reasons but that isn't going to happen anytime soon.
Why bother when these cases pop out of an action easy as can be? AND shoot fantastic groups at distance with vastly improved ballistics?
METAL FATIGUE.... that's why. What I saw in a report on R&D for a new receiver was the duty cycle of the metal itself. When kept at standard pressure, the duty cycle was massive.. certainly, more then anyone sport shooting would ever use up. Even someone with access to a belt fed solution would have a hard time breaking the receiver.
Magnum pressure, the duty cycle dropped significantly but still more then a few lifetimes of shooting.
Proof pressures and things fell a ton... to the point that someone could easily shoot that many rds in a few years.
Higher then that and duty cycle was scaringly short.
I have no way to know how the massive range of materials and designs in modern actions will respond to wear and tear but there is no doubt that excessive pressure stresses the STEEL in the action.
How hot you load to is a personal thing but be aware that a failure has implications to you, the ones around you and the places that we want to shoot at.
YMMV.
Jerry
