Somethings I believe Every shooter Reloader ough to KNOW

[BushMaster-15]

Short read informative correlation CUP - PSI formula with Standard deviation ,so it's NEVER EXACT . Long of it short ,NEITHER measuring systems are 100% accurate ,so goes reloading VARIABLES . There most certainly is a mathematical formula for comparison ,Yet 1 Way .

The bottom line is that the random error associated with the CUP system has a
standard deviation of about 2,000 PSI (correct usage), and the piezoelectric system has a
standard deviation of about 1,300 PSI.

https://www.shootingsoftware.com/ftp/psicuparticle2.pdf

 

[GeoDudeFlorida]

Short read informative correlation CUP - PSI formula with Standard deviation ,so it's NEVER EXACT . Long of it short ,NEITHER measuring systems are 100% accurate ,so goes reloading VARIABLES . There most certainly is a mathematical formula for comparison ,Yet 1 Way .

The bottom line is that the random error associated with the CUP system has a
standard deviation of about 2,000 PSI (correct usage), and the piezoelectric system has a
standard deviation of about 1,300 PSI.

https://www.shootingsoftware.com/ftp/psicuparticle2.pdf

This is why I like to remind people - and am constantly insulted for doing so but, I just consider the source - that in many ways, the older, pre-pressure data is more useful to the handloader than either CUP or PSI simply because it tests loads in over-the-counter, commonly used and well-documented firearms. Unless the shooter is using a universal receiver and under-spec' pressure barrel for their load testing, the PSI data is virtually useless. All it tells the handloader is how much pressure was recorded in the test barrel, on that day, using that strain gauge. It tells us nothing about the load in a commercial barrel with an "average" chamber in a production-grade receiver.

Add to that, in the pre-pressure test days of loading development, ACCURACY was the primary goal of testing. Which is why the older tables typically included notes about the load's performance in their testing, like, "most accurate," "hunting load," and/or "factory replication" annotations. Take it all in with a grain of salt and a dash of pepper.

 

[BBarn]

SAAMI standards were established for the compatability and safety of arms and ammunition. Member manufacturers comply with the testing procedures and requirements in an attempt to ensure that compatability and safety.

Reloaders who follow SAAMI pressure tested recipes are very likely to end up with ammo that is safe to shoot in any SAAMI compliant firearm of the appropriate clambering. The use of test barrels for developing those recipes also means that the velocities (and pressures) achieved in most firearms may be less than those measured during the lab testing.

Some experimenters will exceed published data in attempt to improve performance. In some cases those loads will be safe in their guns. In other instances guns will be damaged in such quests.

 

[Seedy Character]

One manufacturer does NOT measure pressures on the ammo.
When brass will not last for 10 loadings, they consider the round as overloaded.

I do like having pressures listed, for quick comparison between powders. Highest pressure doesn't mean highest velocity.

Just another point of data to consider.

 

[westernrover]

Pressure will always be relevant as long as the manufacturers of over-the-counter, commonly used and well-documented firearms are proof-tested according to SAAMI and/or CIP standards defined by units of pressure.

It is understood that the pressure units of a load are not the primary criteria for a successful load.

In practice, I load rifle cartridges for a velocity node and I'm not likely to look for a node anywhere near extreme pressures for the cartridge. With handguns, I am looking for a goal velocity based on bullet design rather than a node. I do load to more extreme pressures because fast powders are generally more consistent and accurate. If I can't obtain the goal velocity without the brass sticking, then I will have to move to a slower or more progressive powder.

 

[higgite]

One manufacturer does NOT measure pressures on the ammo.
When brass will not last for 10 loadings, they consider the round as overloaded.

And that manufacturer is?

 

[BushMaster-15]

The correlation between CUP and PSI is fairly constant ,given the std. deviation allowable variable . ( Without it FORGET IT ) !.
I learned that way back in college as Math is an exact science and ALL experiments have variables . Again with Hercules it was as close as possible given Std. variables within a chemical batch on any given day . Exact NEVER happened super close YES ,sometimes .

MY rule 50K CUP /62K PSI , I know the Math rule is 50K CUP 60KPSI but I actually witnessed it on several occasions slightly exceeding the stated CUP . Just thought everyone should see the formula .

Another tidbit of info borrowed so I didn't have to type with link . Not all measurements are SAAMI ,either C.I.P. also gums up the works .

https://gundigest.com/gear-ammo/ammunition/223-vs-5-56

Let’s construct our own cartridge, just so we can remain theoretical for the moment. The “.30 Zoomer Magnum” has a maximum average pressure (MAP, or the allowed peak) of 50,000 CUP. We use the newfangled transducer to measure the standard reference load (in this case, 42 grains of “XYZ” powder under a 183-grain soft-point) and come up with 57,000 PSI. The “new” MAP for the .30ZM is now 57,000 PSI, where before it had been 50,000 CUP. But the actual pressure has not changed, we are simply using a new yardstick to measure it with.


Then we run into problems. In checking loading data, we find that some of the data wasn’t as “clean” as we thought. An example: using “123” powder under the same 183-grain soft-point, we had found that we could get 100 fps more and still only see 50,000 CUP pressure. With the new transducer and seeing things in thousandth of a second slices, we see that, yes, the main pressure peak is only 57,000 PSI, the allowed max by the new yardstick, but we also see a second, higher, spike from the bullet hitting and stalling in the rifling. That spike comes in at 63,500 PSI, well over the maximum allowed. So, we have to throttle back the load data, and all of a sudden “123” powder loses its 100 fps advantage.

There was no way to formulate an equation for a “universal translator” of CUP to PSI. Give it up, forget the conspiracy theories your gun club buddy tells you, just accept the new info for what it is.

The NATO spec for 5.56 has a higher “ceiling,” but it’s also measured slightly differently, and, again, there is no handy-dandy conversion. The SAAMI method measures pressure at the middle of the case. NATO (the European measuring group is known as C.I.P.) measures at the case mouth. A CIP-spec 5.56X45, measured at the case mouth, shows a pressure of 62,000. Measured at the case middle, as SAAMI does, it shows 60,000 units of pressure.

 

[denton]

When I wrote that article, I already had a strain gauge system, and was wanting a safe load for my milsurp 6.5x55. The article was a byproduct of that effort.

 

[jmorris]

I am not sure it matters to the average reloader, who doesn’t have the ability to measure either.

There are many variables involved and we all know the chances of getting identical velocity of any book load. It would be unrealistic to think you’re hitting the same peak or average pressure, on a different day, with a different lot, with a different gun…