Re: cartridges and pressures

19 December 2004, 10:37

<eldeguello>

Denton, I have no questions! My (narrow) mind is made up. Please don't confuse me with the facts!

19 December 2004, 10:04

<eldeguello>

Quote:

I downloaded hodgdons reloading manual. My question is what makes these cartridges more suitable to operate a such high pressure and the other standard cartridges not suitable??

Absolutely NOTHING!! The short magnums MUST BE loaded to such pressures to "equal" the bigger ones' velocities! If you have an action that will withstand these pressures, and it will handle the bigger magnum cases, you can load the bigger ones to equal presssures with slower powders, AND BEAT THE PANTS OFF those short fatties. It's all an advertising scam!!< !--color-->

Quote:

Also what determines how much pressure a cartridge can safley operate at??

The cartridge case is the weak link in any rifle/action system. If the brass is of equal thickness and drawn to the same tensile strength, the size and shape of the cartridge have NOTHING to do with how much pressure it will safely hold. The ONLY way to really make a qyuantum leap in the strength of the rifle/cartridge system is to use STEEL cases! (This has been done, but the increase is not worth the trouble of making cases from steel.)< !--color-->

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!!

19 December 2004, 11:11

denton

ROFLMAO!!

I can respect that!

19 December 2004, 09:22

Dutch

Just to point it out explicitly, there is nothing special about the 65,000 PSI limit that the WSM's and RUM's operate under. It is the same pressure limit as the 270 Winchester (introduced in 1920, IIRC), and the 308 (introduced in the 64, IIRC).

Given the improvements in steel manufacturing (outside of Finland, apparently), such pressures are well within the safety envelope. JMO, Dutch.

19 December 2004, 11:27

cummins cowboy

what was the orginal standard .270 win load with a 130grn bullet? in fps. I do know for some reason the 270win in particular is being downloaded, could this possibley be to make the 270wsm look better?? Cause playing with the charts If I make a full house 270 handload with some RL 22 in it the 270wsm is pretty redundent in performance to the 270win. It looks as if all the short mags are doing is operating at higher pressures, whats so new and exciting about that, especially if the 270win brass and 270wsm are rated to the same pressures, If I am understanding what is being said correctly??

18 December 2004, 22:22

vapodog

ALF:

Quote:

Vapodog:

The conversion factor from CUP to PSI is not constant.

It actually gets bigger the higher the CUP value

I'll accept that at face value but until I find a better way of comparing the two I'm using the best I've got.....and this is still the best I've seen.

If you have a better chart or formula I'd love to see it.

18 December 2004, 17:36

vapodog

Quote:

what if steel is used?? also what is the difference between cup and PSI

Steel HAS been used and is still available to a few with a .30-06.....WWII ammo was loaded in some steel cases.

I suspect it might haise hell with loading dies.....I've never tried it.

Thanks to denton you can conver PSI to CUP by the formula:

PSI=(1.516 X CUP) -17902

Just off the cuff guessing one might safely run pressures to 80,000 PSI in a steel case.....I suspect there's a great reason one of the major arms companies is not making it!!

18 December 2004, 17:37

denton

SAAMI specs are not perched on the brink of catastrophic failure. They represent an economical operating point for the firearm and brass. There isn't much to add to the good advice already posted.

Quote:

also what is the difference between cup and PSI

See the CUP/PSI article by the little known and much underappreciated author at... http://www.shootingsoftware.com/tech.htm

18 December 2004, 18:34

ALF

.

18 December 2004, 19:35

lawndart

I spent a good part of today wading through the SAAMI protocols for centerfire rifle ammunition.

Here is the conversion formula that showed up as most prominent to my eyes:
To convert from a Remington receiver to a Universal receiver costs $6,200 USD. The good news is that you get to keep the Remington. Each pressure barrel is $400.00 - $650.00. Add in the cost of the specified instrumentation and you have enough change back from a $10,000 bill to buy one cheeseburger and a coke, no fries.

Alf, I was wrong about standardized ammunition the other day. A given caliber is available from Federal, W-W, or Remington. They have them divided up.

SAAMI is a bit behind the times in some respects. I have some inquiries out to see if they do indeed recognize strain gauge data.

Also, as denton has observed and written, SAAMI specifies that ammunition be "conditioned" by sitting in a controlled environment (70 degrees F +/- 2 degrees, 60% humidity +/- 5%), but they make no mention of barrel temperature

.

19 December 2004, 06:06

denton

ALF...

I think you might enjoy the article. It clears up some of the issues.

You can't use a conversion of the form PSI = m x CUP. You have to use a conversion of the form PSI = m x CUP + b. Once you add the extra term, it all works.

CIP, the European equivalent of SAAMI, does their pressure measuring at the mouth of the cartridge, so their CUP and PSI numbers are not the same as ours. However, they do publish both CUP and PSI data off just a single test, using a conversion just as I have described... constants of the formula are a little different, but it's the same process.

19 December 2004, 10:24

denton

eldeguello, my friend, please take time to read the article. I think it will answer your questions.

Here's the mathematical proof that there MUST be a formula that connects PSI and CUP. You can write an equation that expresses peak pressure as some function of copper pellet deformation. You can write another equation that expresses peak pressure as some function of the voltage induced on a piezoelectric crystal. You can invert the copper pellet equation, and substitute it into the piezoelectric equation, which gives piezoelectric output as a function copper pellet deformation. If you can do that, then the only thing remaining is to discover what the PSI vs. CUP formula is, because we have already proved that it exists.

CIP in Europe does this routinely. They take only piezo data, and convert it to CUP. That lets them publish in both types of units, with only one test.

The sort of "spanner in the works" is that neither the CUP method, nor the piezo method is really all that good. There is a fair bit of random noise in both measurement systems. By the method I have used, the curve has the benefit of many samples, and random noise is reduced by the square root of sample size. The resulting conversion curve is pretty good, for rifles, over the range 28-65 KPSI. It does not apply to pistols, or shotguns, or pressures outside the range that has been investigated.