cartridges and pressures

18 December 2004, 15:43

cummins cowboy

I downloaded hodgdons reloading manual. I noticed that the short action ultramgs and WSM cartridges are operating at way higher pressures than the rest of the calibers. My question is what makes these cartridges more suitable to operate a such high pressure and the other standard cartridges not suitable?? Also what determines how much pressure a cartridge can safley operate at?? I know the rifles action is one, but besides that

18 December 2004, 17:05

Clark

The same brass is used for a 10 kpsi cartridge as a 65 kpsi cartridge.
The cartridge itself has little variation in pressure potential, with rimless being capable of less. My over pressure tests to see what happens show the 10mm pistol cartridge and the 7.62x39mm rifle cartridge being amoung the lowest maximum real limit of pressure.

Cartidges like the 32 S&W may be rated at 10 kpsi, but can take allot more than a cartridge like the 270 that is rated for 65 kpsi.

What does it all mean?
It is the guns that have ratings, and the best of the best I have tested is the 98 Mauser.

18 December 2004, 17:08

DuaneinND

The construction of the cartridge also is a factor in what the safe working pressure will do. The case is the weakest link in the pressure question, so a case that is designed with more strength in the web area and thicker stronger case walls can have a higher safe working pressure. The Ultra Mag, WSM, and their shorter versions are built and designed with very little body taper, heavy duty web areas and thick stiff case walls. The PPC cases, Remingtons BR cases, and cases based on the 308 case are also designed to work at higher pressures.

19 December 2004, 16:40

DuaneinND

I think you are beginning to understand. The only thing to remember is that not all brass is manufactured to the same specs. If the load you are shooting causes the primer pocket to loosen up your loads are TOO HOT, if you can load and fire the same cases 5-6(I prefer 10) times with no detectable expansion chances are you are safely within the working pressure of the case. The drawback to high working pressures can be difficult extraction, loads that are finre at 40* can cause problems at 80 or 90 degrees.

www.duanesguns.com

21 December 2004, 03:15

<eldeguello>

Denton, what I guess I wanted to say is that the relationship between C.U.P. and PSI is not linear. That is, the relationship varies from one cartridge to the next, and also at various pressure levels, even in the same caliber.

For example, if C.U.P. and PSI are the same number when pressure testing near-max. loads in the .45/70, (and they are!!) these two measuring systems will NOT produce the same relationship when the .30/'06 is tested. And this same thing is true again when the 7mm Rem. Mag is tested. So, if a formula exists that will let us accurately relate C.U.P. to PSI in a given cartridge AT A SPECIFIC PRESSURE LEVEL, this formula will NOT work with other cartridges nor when the pressure level changes significantly even in the SAME CARTRIDGE. - each cartridge, (and each pressure level), will require its' own formula.

21 December 2004, 03:25

<eldeguello>

Quote:

what was the orginal standard .270 win load with a 130grn bullet? in fps.

If memory serves, it was around 3140 to 3170 FPS, (published factory velocities).

Whether this speed was ever actually attained in Joe Blow's rifle, we don't really know, because in those days no-one except Phil Sharpe had a chronograph.

And a lot of early factory velocities were taken from a 30" barreled pressure gun in a lab, not in a sporting rifle!

Now, what is the real advantage to the real short, beltless magnums? Well, 1. They have no belts, so should headspace a little better for the first shot, escaping the case-stretching problems belted cases often suffer from (due to less-careful chambering - no fault of the CARTRIDGE DESIGN!!) 2. Short, fat powder columns seem to contribute to ignition uniformity, and hence, accuracy. 3. They can be chambered is short-action rifles which have stiffer actions, hence better accuracy. 4. Short-action rifles can be made shorter, lighter, and easier to handle.

Any disadvsantages? 1. Have to operate at higher pressures to get claimed ballistics - may be a problem in Africa, TX, AZ, or in other hot locations.

2. Fat cases may reduce magazine capacity.

(Not a problem for us single-shot guys!!)

21 December 2004, 03:33

Dutch

That, and there was no such thing as 4831 back then. IIRC, 4064 was the slowest available powder........ Yowzaa! Dutch.

21 December 2004, 03:45

<eldeguello>

Quote:

Quote:

... ALF is correct, the difference between CUP and PSI varies from one cartridge to the next, in a very unpredictable way. For example, in the .45/70, C.U.P. and PSI are equal!!

If anyone ever mentions that I "agreed" with eldeguello, I'd certainly not appreciate it.

Hey HOT CORE!! What is it you disagree with me about? What I say, or the way I say it? You know, writing in English is hard!!

21 December 2004, 10:01

<eldeguello>

Got a PM from Denton - this makes what he said easier to understand. Hope he doesn't mind my posting it.

"Nursing the flu here... back to the OJ and another nap as soon as I

finish this.

The relationship between PSI and CUP is actually quite linear over the

region of most interest. It gets a little unpleasant outside that

range. But it is not a simple multiplication, either. That's the part

that seems to derail everyone. The CUP system does not start to yield

at zero, but the piezoelectric system does read zero at zero PSI. So

the two have different Y intercepts, and you need an additive constant

in the equation.

The individual points are a bit noisy, because they ain't

points--they're ellipses. Neither the CUP nor the piezo system SAAMI

uses is very precise. There is a fair bit of random noise in both

systems, so you get a fair bit of uncertainty in where any point on the

graph belongs. If you see it in perspective, it's not really too bad.

I'm convinced that no two labs can reliably generate the same pressure

for the same load within 2,000 PSI anyway.

I don't have a way to post pictures on the board, but thought you might

be interested in seeing what it really looks like.

Cheers!"

Sorry to hear about your flu - hope you recover before Christmas!

Thanks for the explanation & graph!!

Is it perhaps the required "additive constant" that makes this equation difficult for a lot of people to comprehend?

21 December 2004, 13:09

Hot Core

Quote:

... Hey HOT CORE!! What is it you disagree with me about? ...

Hey eldeguello, Actually, I think we agree about a lot. Just tossing the needle your way to keep you on your toes and the pot stirred a bit.

---

Didn't want to see you standing alone on an issue where you are totally correct. Apparently we both dislike seeing folks getting sucked into believing the totally incorrect notion that ANYONE has come up with an "accurate conversion" of CUP to PSI. If it was possible to do so, SAAMI and Hodgdon would have it available for use by the general public.

There is a lot of bad info available on the net for people to have to wade through. If you (and I) are able to convince them about how wrong the thought of an "accurate" conversion is, then we have helped them.

As I think more about it, it seems some folks have been willing to accept "inaccuracy" in certain aspects of their Reloading, since some of their toys require "Fudge Factors" to get within 20,000PSI of reality. Once they shrug off inaccuracy as being "OK", they fail to consider how something of this nature has the potential to "mislead" a Beginner down the wrong Logic path.

In order for a System to be a good one, it has to be both accurate and withstand challenges to it's overall function. Here meaning with every Cartridge available. The CUP to PSI "conversion idea" simply fails in both regards.

Best of luck to you eldeguello and a Merry Christmas!

21 December 2004, 13:59

denton

As usual, Hot Core, you have no facts, no figures, and no physics. You have an unfounded assertion, backed by nothing but your own opinion.

Quote:

If it was possible to do so, SAAMI and Hodgdon would have it available for use by the general public.

What bodily orfice did you get this out of? If you had been thorough, and contacted some of the European companies, you'd have found that they routinely do this. So there you have a concrete example of someone doing exactly what you say can't be done. If you had called them, instead, would you be announcing to the world that the conversion exists, and works?

Or, have you found a flaw in CIP's procedure? If so, let's hear about it. If it doesn't work, you should be able to explain why. Come on, Hot Core, tell us what's wrong with their professional procedure.

Dr. Brownell had a PhD in physics. Oh, let's see... you claim to be an EE, but can't answer extremely simple questions about electronic circuit design. Yeah, the fake EE must qualify you for more credibility than PhD physicists, who studied the issue, and published their scientific work. Yeah, a fake EE carries a lot of credibility.

My data and analysis are posted for all to see. Let's see your data and analysis.

You advocate the PRE method, which can just barely resolve 20,000 PSI differences, and then piss and moan mightily that the the PSI/CUP conversion can only land you within 3,000 PSI, and is therefore inaccurate and invalid. Hmmm... what's wrong with that picture? I think it's called swallowing camels and straining at gnats.