How do they measure cup pressure

[Reloadron]

Another good read on all of this, including all of the numbers is ANSI/SAAMI Z299.4 – 2015. The .4 suffix points to center fire rifle. ANSI (American National Standards Institute) and our friends at SAAMI (Sporting Arms and Ammunition Manufacturers' Institute) have compiled the document(s). What can be found here is the test methods and procedures as well as the equipment used for chamber pressure testing. Important also is the actual sensors used, Series 117B Charge Mode Conformal Ballistic Sensors. Called a "conformal" sensor because of how it conforms to the radius of the cartridge at a determined location. Anyway the first link to the ANSI/SAAMI document is some interesting material.

Ron

 

[Aguila Blanca]

There isn't agreement using the CIP method in Europe, for which the copper crusher gave the .223 Remington a maximum of 53,700 psi and their channel transducer maximum gives 62,400 psi (both rounded to neares 100 psi), a bigger difference than our equipment produces.

If I remember correctly, the difference is at least partially accounted for by the fact that the European test locates the transducer at a different point in the chamber than the U.S./SAAMI test.

 

[Aguila Blanca]

I really don't see either as more exacting. Looking at most loading manuals they point out how their data was obtained. Just as an example Hornady 9th Edition 308 Winchester they point out Rifle: Winchester Model 70, Barrel: 22" 1:12 Twist, Case: Hornady / Frontier, Primer: Federal 210, Bullet Diameter: 0.308", Max Case Length: 2.015", Case Trim Length: 2.005". My Speer #12 list much different test conditions and has different results. If we leave the bullet smiths and look at the powder guys the same sort of results will apply. All of this simply means that on a given day under given test conditions, methods and procedures here is the data we got. Two identical rifles will likely give different results to a point. So I really do not see either the powder guys or bullet guys being more exact than the next. I do like to know how their data was obtained but that is more just a me thing.

Lyman's data are obtained using a test barrel in their own range, not standard firearms.

 

[F. Guffey]

It must have been 15 years ago I had the opportunity to acquire cases that had been used for testing, There had to be 100,000 cases. Some of the cases had evidence of having been fired in a CUP test barrel. I was asked if that would bother me and of course I said no. I also said I had no interest in the cases because I had and still have more cases that I will ever need and some of the ones I have were fired in a test barrel.

I did express an interest in the cases if I was allowed to measure the cases before and again after firing. I have always thought when testing something had to be ion the chamber when the cases is fired, and for the same length of time I have always know the case was in the chamber when fired.

In the beginning it was suggested the reloader learn to measure the diameter of the case head. It was suggested the case head expands .000250 when fired with factory loads. All of the cases that were fired were from a factory and they had nothing to gain by blowing up cases and chambers' therefore there was little interest in measuring the case head of the fired cases.

I have test fired receivers that were sold to me as being suspect, I measured the diameter of the case heads before firing and after firing to prove the cases were loaded heavy. Nothing suspect about the receivers and or the cases, the flash holes expanded, the primer pockets expanded, the case head shortened from the cup above the web to the case head and the case head expanded.

And then there is that thing about case head separation with all of this other stuff going on.

F. Guffey

 

[Reloadron]

Aguila Blanca:

Lyman's data are obtained using a test barrel in their own range, not standard firearms.

Least we forget our friends at Lyman. Yes, the Lyman 49th Edition for example, for the 308 Winchester points out Firearm Used: Universal Receiver, Barrel Length: 24", Twist: 1:10, Groove Diameter: .308". So they use a Universal Receiver test jig and they also call out their Test Components.

Lyman, also depending on caliber does use commercial firearms. Just as an example Lyman 49th Edition, 223 Remington Test Specifications for the Firearm Used they call out a Universal Receiver having a 24" barrel length 1:12 Twist and they also call out a Colt AR 15 with a 20" 1:7 Twist. They test a wide range of bullets.

The Lyman manuals are an endless wealth of really good information. They also spell out if their pressure units are CUP or PSI, all good stuff.

Ron

 

[T. O'Heir]

"...psi and cup are totally different..." And there's no mathematical formula to convert one to the other either.
"...for both 223 and 5.56..." Yep. Neither SAAMI or CIP(Permanent International Commission for the Proof of Small Arms. With member countries.) has no 5.56 NATO standard because its a NATO standard. SAAMI is a voluntary American small arms manufacturer's standard.
CIP does .223 REM at a higher max pressure than SAAMI though. Mind you, CIP standards generally are higher than SAAMI's. http://kwk.us/pressures.html
"...not standard firearms..." Most ammo tests are done with a Universal Receiver. The only time they are not is with really odd/old/rare cartridges. The whole point of SAAMI (and CIP) is to have one set of standards ammo and firearms manufacturers can use so all of 'em are making stuff the same way and we can use any .223(for example) ammo from any maker, in any firearm chambered in .223.
"...The Lyman manuals are..." Yep. Written in English vs technocrat too.
"...worked up watching for pressure signs..." Hasn't been done like that for a very long time by anybody. Far too much risk of a liability suit.

 

[FrankenMauser]

Here you go:
R-P .444 Marlin cases that were used in a copper crusher testing apparatus.

Sorry, none of them were empty. There's also a well-defined ring on the inside of the cases, where the case wall was attempting to shear.

(As you might have been able to infer, based on oddities in the photo and the (limited and truncated) load data on the box, I only use these for shot loads. ...Not because I am afraid it has been compromised too much, but because it's the only R-P brass that I have for the cartridge and I don't want to have to worry about load data for Hornady vs R-P brass. I do know several people whose only .444 Marlin brass is from this same lot, however, and they run it with full power loads.)

 

[74A95]

Correct psi and cup are totally different. This is part of the worry people have about shooting 5.56 in a 223 chamber. 223 standard pressure is CUP. 5.56 is measured in PSI.

223 is measured in CUP (limit 52,000 CUP) and psi (limit 55,000 psi).

https://saami.org/wp-content/uploads/2018/01/Z299-4_ANSI-SAAMI_CFR.pdf

The PSI max for both 223 and 5.56 is 55,000 PSI.

5.56 has a higher limit (62,366 psi) than 223. https://en.wikipedia.org/wiki/5.56×45mm_NATO#5.56mm_NATO_versus_.223_Remington

Western's load guide has separate data for 223 and 5.56, each with different pressure limits.
http://www.accuratepowder.com/wp-content/uploads/2010/09/WesternLoadGuide1-2016_Web.pdf

 

[Jim Watson]

P/V barrels for SAAMI compliant testing are held to very close tolerances.
One reason manual velocities are usually higher than you will get out of a real gun, chamber and bore are tight.
I think blueprint minimum -0, +.0005" but you can look it up to be sure.

Some gunzine writer had a deal with a lab and got their barrels after they had been "worn out" with maybe 800 shots. Cut off at the gauge port, rethread and rechamber and he had a very fine barrel for little money.

There was a lab that would pressure test your loads in your barrel.
The trick was that they used the old British setup with a crusher in the bolt head so they could get a reading without drilling a hole in the barrel.
They just had a hatfull of thread adapters so they could take your barrel off its action and put it in their universal receiver.
Readings were not directly comparable to chamber hole gauges, but reference ammo is available, so they could return a comparison of your load to maximum.

 

[big al hunter]

5.56 has a higher limit (62,366 psi) than 223.

Read further down the page you linked. 62,366 is the CIP standard pressure. NATO max pressure for 5.56 is 55,000 max. And the SAAMI max is also 55,000

Because CIP and SAAMI use different methods to test they get different numbers. If they used the same method the numbers would match up as well.

 

[74A95]

Read further down the page you linked. 62,366 is the CIP standard pressure. NATO max pressure for 5.56 is 55,000 max. And the SAAMI max is also 55,000

Because CIP and SAAMI use different methods to test they get different numbers. If they used the same method the numbers would match up as well.

Your last statement is contradicted by multiple resources. The 5.56 has a higher pressure limit than the 223, based on various other sources and Hornady, Speer and Western Powders.

https://www.americanrifleman.org/articles/2013/3/4/223-remington-vs-556-whats-in-a-name/
https://www.shootingillustrated.com/articles/2018/7/28/556-nato-vs-223-rem-whats-the-difference/

https://www.luckygunner.com/labs/5-56-vs-223/

Numerous sources warn against shooting 5.56 military ammo in gun chambered for 223.

http://www.hornadyle.com/resources/...ence-between-556-nato-and-223-rem-ammunition/

SAAMI says that 5.56 military ammo is dangerous in firearms chambered for 223.
https://saami.org/wp-content/upload...Site-and-Brochure-Master-Revised-5-7-2018.pdf

 

[F. Guffey]

As I said I had the opportunity, another member purchases the test cases in barrels and sold them through one of the gun auctions. Not one complaint.

F. Guffey

 

[big al hunter]

Your last statement is contradicted by multiple resources. The 5.56 has a higher pressure limit than the 223, based on various other sources and Hornady, Speer and Western Powders.

You do not understand the issues. I did not say it was safe or not to shoot 5.56 in a 223 chamber.

The cartridges are identical in size and pressure standard. That does not mean that they are loaded the same. The difference is in how the chamber is shaped. The 5.56 has more room in the throat. If you shoot a 5.56 cartridge in a 5.56 chamber you should not exceed 55,000 PSI. If you shoot the same cartridge in a 223 chamber it may be over 55,000 PSI as the chamber is somewhat tighter.

The same issues can be seen in handloaded ammunition. A load that is safe in my 30-06 with a bullet seated to .002 from the lands might be over pressure in your 30-06 because your lands are .005 closer to the bolt.

Every ammunition manufacturer produces ammunition that is below the max pressure in the tightest chamber within accepted tolerances. Therefore it is safe in any chamber that is in spec. It will however be under pressure in most rifles because they are not all built to the minimum size in the tolerances. That is why we can usually tune our handloaded ammunition to a specific rifle and improve the velocity and accuracy while still being safe doing so.

 

[JohnKSa]

The PSI max for both 223 and 5.56 is 55,000 PSI.

Not according to Black Hills Ammo.

Sept/October American Handgunner
Black Hills Ammo-Family Values--No Compromise Quality
by Wayne Van Zwoll

"We do distinguish between .223 and 5.56 ammunition," emphasized Mike Wright. "Per SAAMI specs, the 5.56 NATO is loaded to higher pressures. You may see identical velocities in our data. That's because we chronograph 5.56 ammo from 20" barrels, .223 from 24". BHA does not recommend use of 5.56 ammo in barrels with .223 chambers.​

https://www.americanrifleman.org/articles/2013/3/4/223-remington-vs-556-whats-in-a-name/

According to Jeff Hoffman, the owner of Black Hills Ammunition, military ammunition can be expected to hit 60,000 p.s.i., if measured on a Sporting Arms and Ammunition Manufacturers’ Institute (SAAMI) mid-case system. Black Hills loads both 5.56x45 mm and .223 Rem., and Hoffman was a tremendous help in researching this article. He also provided these pressure specifications for the cartridges. The .223 Rem. mid-case transducer maximum average pressure is 55,000 p.s.i., while a 5.56x45 mm measured with a case mouth transducer has a maximum average pressure of 58,700 p.s.i.​

According to Black Hills Ammo, when .223 and 5.56 are both measured under identical conditions, using the mid-case transducer system, .223 records maximum average pressures of 55,000psi vs. 60,000psi for 5.56.

 

[74A95]

The cartridges are identical in size and pressure standard.

They simply are not. Re-read the linked resources.

 

[big al hunter]

There are so many sources out there. Most of them don't note which system is used for the pressure testing. It makes a difference. Below are the NATO standard max pressures for 5.56. EPVAT is the military standard test with a hole drilled in the throat of the chamber, reading after the bullet passes it. SCATP is the SAAMI method using a transducer inside the chamber. Where you take the pressure changes the max amount. If the test method is not specified in an article I would assume that the writer has a degree in writing, not engineering and has no clue that the difference exists. The Black Hills quote says that the 223 is mid case transducer. The 5.56 is case mouth transducer. Where the test is taken changes the max rating number. The same loading tested with 3 different systems will yield 3 very different numbers. We can't compare apples to oranges.

Maximum pressure (EPVAT)
430.00 MPa (62,366 psi)

Maximum pressure (SCATP 5.56)
380.00 MPa (55,114 psi)

 

[JohnKSa]

There are so many sources out there. Most of them don't note which system is used for the pressure testing.

Right. That's why the Black Hills information is not only simple to understand but also conclusive.

They're measuring the two cartridges on exactly the same equipment using exactly the same technique at exactly the same point in the cartridge. That allows one to see how much difference there really is with no possibility for confusion.

The Black Hills quote says that the 223 is mid case transducer.

Correct. HOWEVER, Black Hills measured both cartridges using the mid case system to provide an apples-to-apples comparison.

"...military ammunition can be expected to hit 60,000 p.s.i., if measured on a Sporting Arms and Ammunition Manufacturers’ Institute (SAAMI) mid-case system.."

"...The .223 Rem. mid-case transducer maximum average pressure is 55,000 p.s.i.,..."

When .223 and 5.56 are both measured under identical conditions, using the mid-case transducer system, .223 records maximum average pressures of 55,000psi vs. 60,000psi for 5.56.

 

[big al hunter]

I'm not convinced that they test fired with mid case on 5.56. The quote says "if" and "could expect". That sounds like guessing to me. Then they specifically mentioned that the case mouth max average is 58,700 for 5.56. if they tested it mid case, they would have said " it is"...when tested mid case. And I would venture a guess that they test 5.56 at the case mouth.

It seems to be somewhat linear that the max pressure increases as the testing location moves toward the throat of the barrel. From what I am seeing, mid case is 55,000, case neck is 58,700, and in the throat is 62,366.

Just thinking like an engineer...hate that...I despise engineers most of the time. But working with them makes me think like them.. I think too many numbers are in play from too many sources to get a truly clear answer from anyone other than a SAAMI engineer. Does anyone have a friend at SAAMI that we can talk to?

 

[74A95]

big al, you have your facts wrong and now you're making crap up out of thin air. Sounds like a flat-earther.

If you refuse to accept the facts as stated by people in the ammo industry, there's no hope for you.

 

[JohnKSa]

I'm not convinced ...

That's pretty clear. What I'm unclear on is whether there's anything at all that could convince you.

That sounds like guessing to me.

They load both .223 and 5.56 ammo and yet they don't actually know the pressure differences? They're just "guessing"?

How do you explain this unambiguous statement from Black Hills?:

"Per SAAMI specs, the 5.56 NATO is loaded to higher pressures."

More guessing? What about this clear statement:

"Remember, the 5.56x45 mm already starts out at a higher pressure. "

How do you explain away this unambiguous statement from another ammunition manufacturer that loads both .223 and 5.56?(ATK Federal) ?

http://www.le.vistaoutdoor.com/downloads/technical_bulletins/223VS556.pdf

"Mil Spec 5.56 ammo typically has higher velocity and chamber pressure than the 223 Rem."

Are they guessing too? Is that how ammunition companies stay in business? By guessing about pressures?

What about the fact that in apples to apples comparisons, the loads listed for 5.56 in this loading data has more powder in the 5.56 loadings than the .223 loadings?

http://www.accuratepowder.com/wp-content/uploads/2010/09/WesternLoadGuide1-2016_Web.pdf

Where does that extra powder go between the time it's loaded and the time it's fired to keep the chamber pressures the same?