CIP's Pmax, PK, PE: what do they mean?


#1

I’m reasonably sure that Pmax is the maximum allowable pressure for normal ammunition in a given caliber, I think PE is the proof pressure, but what is PK?
I have the drawing set, but there’s no glossary for us clueless ones…


#2

Berdan,

Not that familiar with CIP but I think you about got it right.

From what I understand, Pmax is the nominal maximum pressure, PE = 1.25X Pmax and is the mean proof pressure, and PK = 1.15X Pmax and is the maximum statistical individual pressure.

As a note, the CIP unit of pressure is the Bar and one Bar = about 14.5 PSI.

Dave


#3

Thanks, DaveE!

The definitions make sense to me.

I bounced the numbers off one of their drawings and the PK factor works, but the PE factor was a little low; 1.30 was a closer fit. I’ll check against other drawings, but 1.25 is in the ballpark.

Thanks again.


#4

And, it goes without saying that one should always be very careful when comparing “pressure” units because there are different methods used to obtain them, they are not directly comparable in most cases, and some should not even be called “pressure”.

Ray


#5

Berdan,

I can’t honestly say where I got the 1.25x for proof so I did a quickie search and wikipidia (or some such site) indicates the current rifle CIP proof standard at 125% and the handgun is at 130%. The rifle standard used to be 130% as well, so, if your reference is for a handgun cartridge, your math is good! If it’s a rifle cartridge, perhaps it is to the older standard?

Ray,

Very important comment you make on different test methods and the numbers they produce. I don’t much buy into conversion factors I’ve seen being dead on either. The advent of modern electronics has made pressure testing much more accessible and that should only get more so in the future. I do enjoy looking back at old loading data and comments on assumed pressures developed. It was so simple back when…if you could open the bolt and the primer wasn’t blown out, all was good!

Dave


#6

DaveE:

Yep, the drawing I used for comparison was for a pistol round. Thanks for taking the time to post an update. The muckety-mucks at CIP didn’t respond to an email. I’m much more comfortable now with a little project I’m about to embark on. I know what you mean about maximum loads; an acquaintance figured the “real” load was one that popped primers consistently.

Ray:

I agree, you can’t really relate CUP (or LUP)to PSI. I’d like to see SAAMI post data in both. But, bars can be converted to PSI (Or maybe it’s bars to bistros, I forget which).


#7

Here are the abbreviations from the 1990 edition of the CIP tables. The pressure abbreviations are at the bottom of the page.

Pmax = Mean maximum pressure (bar).

Pk = 1.15 Pmax = Maximum individual statistical pressure (bar).

PE = 1.30 Pmax = Mean proof pressure (bar).

Cheers,

Schneider.


#8

Schneider:

Formidable!

Thanks so much!