How do they measure cup pressure

[JohnKSa]

The 5.56 is listed under EPVAT. The 223 is listed under CIP. The method used is the same, therefore it is apples to apples.

I don't believe that EPVAT and CIP use the same measuring method.

https://en.wikipedia.org/wiki/NATO_EPVAT_testing

"Unlike the civilian C.I.P. test procedures NATO EPVAT testing procedures for the "NATO chamberings" require the pressure sensor or transducer to be mounted ahead of the case mouth. "

"Due to NATO EPVAT using technically differing proof test standards than SAAMI and C.I.P., EVPAT pressures cannot be directly compared with SAAMI and C.I.P. pressures."

In your qoute it stated that Black Hills used case mouth transducer location data.

Actually, that part of the quote just says that Hoffman provided specs for the two cartridges. It doesn't explicitly state anything about their methods--it only tells what the specifications are.

"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."

But I believe it would be very easy to confuse the numbers from different methods of testing.

I just find it too hard to believe that two different ammunition manufacturers are "confused" or "guessing" about pressures on cartridges that they manufacture.

[big al hunter]

I just find it too hard to believe that two different ammunition manufacturers are "confused" or "guessing" about pressures on cartridges that they manufacture.

I don't think the manufacturer is confused. I think the readers are confusing the numbers, not realizing the difference. I believe that they are loading and testing with the case mouth transducer knowing that it is safe. When someone says the phrase " I would expect to see" , it sounds like an educated guess.

"Due to NATO EPVAT using technically differing proof test standards than SAAMI and C.I.P., EVPAT pressures cannot be directly compared with SAAMI and C.I.P. pressures."

Thank you for taking the time to research it and find the difference. I was surprised to see the numbers were the same with the difference between the two methods when I was researching. It has something to do with the transducer being exposed to the burning powder and not insulated by the case . There is a pressure anomaly caused by this that they account for. And the PSI numbers are converted from MPa, which is the CIP format.

Have you looked into SCATP standards yet? And why they exist?

[JohnKSa]

I don't think the manufacturer is confused.

If they're not confused, and we can accept that they know what they're talking about then we can just take them at their word. Here are two direct quotes from ammo makers that don't get into any complications about pressure measurement techniques.

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

Black Hills
"...the 5.56 NATO is loaded to higher pressures."

[big al hunter]

Give this a good look. Nice short article.
http://www.thegunmag.com/reloading-h...223-remington/

[big al hunter]

This one is a little longer, but more detailed. Good information.
http://ultimatereloader.com/2018/08/...#acceptLicense

[big al hunter]

Google "SCATP 5.56 1984". You should find the military spec in PDF format that is no longer classified that you can download and read. A bit boring until the pressure section. Lots of military standard procedure.

[JohnKSa]

So we're back to Federal/ATK and Black Hills being confused about the pressures of the ammunition they load?

Here's another quote from Black Hills.

“The 5.56 IS a higher pressure/velocity cartridge, but it is made to a military standard, with different test methods, (and therefore is not easily directly comparable to .223 pressures) . . . the general spec for US 5.56 ammo is 58,700 psi max, measured at case mouth. . . Please note this is a different method than SAAMI transducer or copper crusher, as used on commercial ammunition. 5.56 ammunition spec results in ammunition loaded to a higher pressure level than commercial .223, but the test methods specified are different . . .The spec calls for a different pressure test method than SAAMI spec ammo, and is not directly comparable . . . “

It would be interesting to see a detailed explanation of the differences between the SCATP and SAAMI pressure measuring techniques and a careful explanation of exactly how the two pressures are quoted. Until we have that, it seems that comparing SCATP and SAAMI numbers directly is misleading based on unambiguous statements from ammunition manufacturers.

One interesting point I noticed in the 5.56 military pressure specs based on SCATP is that while they specify the average pressure at 55,000psi, they seem to allow individual cartridges to test as high as 61,000psi. I can't see any sort of comparable statements in the SAAMI specs, but again, it would be interesting to get a detailed explanation of the differences. It seems clear that they are similar but it is equally clear that they are not identical.

[big al hunter]

One interesting point I noticed in the 5.56 military pressure specs based on SCATP is that while they specify the average pressure at 55,000psi, they seem to allow individual cartridges to test as high as 61,000psi. I can't see any sort of comparable statements in the SAAMI specs, but again, it would be interesting to get a detailed explanation of the differences. It seems clear that they are similar but it is equally clear that they are not identical.

Most specifications have an average limit. Military limit appears to be fairly high for a single cartridge, but that would mean that they allow that much below the average as well. I can agree that the two standards are not identical. But they are pretty close .

If you study the SAAMI charts they also have a max average and a max allowed single load in a lot. It is just harder to find than the standard numbers.

Even though the cartridges are loaded to similar pressure, the chamber still makes a big difference. I can see that most loads of 5.56 may not be safe to shoot in most 223 chambers. But it is an interesting topic for discussion.

It would be interesting to see a detailed explanation of the differences between the SCATP and SAAMI pressure measuring techniques and a careful explanation of exactly how the two pressures are quoted. Until we have that, it seems that comparing SCATP and SAAMI numbers directly is misleading based on unambiguous statements from ammunition manufacturers.

I agree, that would be interesting. I can't remember where I saw it, but somewhere I read that the SCATP was set up for US commercial loaders to be able to produce ammo during war time without changing the method and tools that they already used. NATO EPVAT is set up so the commercial loaders in Europe could produce ammo for NATO troops for the same reasons.

And given that the two standard max pressures are less than 1 % different I would think that there is a military math equation from the EPVAT standard in MPa at work. Whereas SAAMI rounded down a little.

I haven't come across any information about case mouth transducer other than the quotes you have from Black Hills. I wonder where they got it from....

[JohnKSa]

If you study the SAAMI charts they also have a max average and a max allowed single load in a lot. It is just harder to find than the standard numbers.

Right, I should have been more clear. When I said I couldn't find anything comparable, I meant that:

1. SAAMI doesn't specify an allowable maximum for any single cartridge--all of their limits are stated in terms of the results of statistical calculations.

2. The maximums they do state in terms of statistical caculations are nowhere near 61,000psi.