.223 vs 5.56 NATO pressure difference discussion

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T. O'Heir

New member
SAAMI Max pressure for the .223 is 55,000 PSI, not 62,000 PSI.
The two cases are identical. The biggest difference is that 5.56NATO is used in MG's. And the Remington very rarely.
EPVAT(Electronic Pressure Velocity and Action Time) and SCATP are just different methods of measuring. SCATP is basically the same as SAAMI. Difference between 'em is 114 PSI.
"...the great CUP/PSI conversion..." There is no mathematical way of doing that. They're different methods of physically taking the pressure.
Go here, about half way down for a good explanation.
https://ultimatereloader.com/2018/08/05/223-vs-5-56-facts-and-myths/
 
U

Unclenick

Staff
T. O'Heir,

SAAMI is 55,000 psi, but CIP and EPVAT use 4300 bar (62,366 psi); but determined by channel transducer systems where we use the conformal transducer system.
 
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big al hunter

New member
. EPVAT(Electronic Pressure Velocity and Action Time) and SCATP are just different methods of measuring. SCATP is basically the same as SAAMI. Difference between 'em is 114 PSI.
"...the great CUP/PSI conversion..." There is no mathematical way of doing that. They're different methods of physically taking the pressure.
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T O'Heir. Go back and re-read the article you linked. It explains that SCATP and SAAMI use the same protocol for testing and therefore have very similar results from the same lot of ammunition tested. The difference shows up with EPVAT protocol using different types of equipment, at a different location on the chamber. Therefore it gives a higher pressure reading of 62,000 PSI for the same lot of ammunition that tested to 55,000 with SCATP or SAAMI protocol.

The key is that both methods (SCATP & EPVAT) are used to test the same cartridge....5.56 NATO. If there is to be true interchangeable arms and ammunition between NATO nation's, then all ammunition and firearms for that ammunition must be assembled to the same standard. Because the American producers don't use CIP/EPVAT equipment for testing the US military created SCATP for domestic ammunition manufacturers.
 
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Unclenick

Staff
It's a good try, but the author got a few things wrong. NATO does not use the CIP method. They use the EPVAT protocol, which employs the same Kistler 6215 transducers as the CIP method, but samples pressure just past the case mouth instead of through a hole in the case wall. That introduces some harmonic ringing that requires a 200 khz band block filter to be added to the output. It also introduces a small pressure drop, but one easily compensated for through use of reference loads. The advantage is it saves them having to drill cases and align holes, making testing a little quicker.

Lake City used the same system for a time until 2012, when, under ATK management, they changed to the SAAMI conformal transducer equipment and standards. This served both to make it easier to get ammo made by commercial ammunition makers in time of war, and it enabled Lake City to make ammunition for the commercial market when the military demand was low (the Federal American Eagle XM193 and XM855, which is actually made by Lake City). SCATP 5.56 has changed over the years to reflect these and other changes. This is why it has designations like SCATP 2015, etc.

The main thing he missed is that the higher CIP and EPVAT peak pressure reflects the SS109 peak pressure, which is ten percent higher than M193.
 
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Bart B.

New member
Firearm chamber pressure measuring systems are much like the 4 different standards for degrees in mils and yards in miles.
 
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Unclenick

Staff
Make that 7 different standards: SAAMI copper crusher, CIP copper crusher, NATO EPVAT copper crusher, U.S. Military Copper Crusher, SAAMI conformal transducer, CIP mid-case channel transducer, NATO freebore channel transducer.
 
M

Metal god

New member
Aren't we arguing..er..pardon, discussing whether we are doing 61mph or 100km? And some people think 100 is dangerously fast???
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I'm stealing that next time this comes up . Best and easiest explanation to understand I've ever heard .
 
T

thallub

New member
Thanks mehavey. i had lost that link.

It's considerably more complicated:

1. There are numerous established .223 and 5.56mm chambers.

http://ar15barrels.com/data/223-556.pdf

2. Contrary to popular notion; not all barrels are chambered by gunsmith school graduates. Most chambering is done by day labor, you get whatever chamber the person wielding the reamer provides.

3. One of my .223 rifles has a tight match chamber. Some US factory .223 ammo will not chamber in that rifle.
 
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Metal god

New member
3. One of my .223 rifles has a tight match chamber. Some US factory .223 ammo will not chamber in that rifle.
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Although true and important to understand . That is not really relevant in the over all point , out of spec or can't get much closer to out of spec is not what the general conversation is about . IMHO we should start and stay with in a good faith argument in these type of talks that we are talking about in spec ammo and rifles . There's always going to be exceptions do to tolerances stacking up in the wrong direction . They don't come up that often and when they do its not because the ammo was tested two different ways .

If I recall isn't most tests done in the smallest chambers to ensure the pressures will work for said small chambers ?
 
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Bart B.

New member
Metal god said:
If I recall isn't most tests done in the smallest chambers to ensure the pressures will work for said small chambers ?
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I doubt they are. Little, if any load test barrel specs are listed with data other than barrel length. Many use commercial sporter barrels and a given load will have quite a range of velocity and pressure across all for a given cartridge.

A SAAMI spec test barrel is the best, but they probably cost near twice what a match grade barrel costs after lapping the bore to specs and drilling holes in the chamber area to install expensive pressure measuring stuff.
 
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Unclenick

Staff
The commercial tests in this country are done in SAAMI standard pressure and velocity barrels whose chambers are cut to match the drawing in the SAAMI standard to within half a thousandth of minimum. So they start out as minimum chambers and I doubt the diameters change appreciably over their testing life, but the throats will grow and I seem to recall running into a reject spec for that which was something like +0.003", but don't quote me on it. I'll have to look at the standard again.

The bottom line is they try to use a minimum chamber as the worst case in pressure testing, but not without some tolerances being involved.
 
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Bart B.

New member
Yes, Unclenick's remarks are good for commercial ammo.

Would be nice if all published load data listed test barrel complete specs. A .002" spread in bore and groove diameters cause quite a spread in pressure and velocity.
 
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Bart B.

New member
Don Fischer said:
And if they listed the test barrel, what would you do different working up a load?
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I would measure my barrel's chamber and bore dimensions to set my expectations for that same load if I knew their test barrel specs.

And if my load's bullet pull force was less than the load data's pull force, I would expect less velocity.

Knowing my powder lot is different than the data's lot, I would expect a 50 fps or more velocity difference for the same charge weight.
 
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Unclenick

Staff
The SAAMI spec gives the number of lands and minimum bore and rifling cross-sectional area. They are nominal groove and bore diameter, so they won't be as fast as a tight Palma bore.
 
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Bart B.

New member
Largest commercial 30 caliber groove diameters I've slugged then measured were Winchester 70 target rifles. One pre-'64 broach rifled barrel 30-06 was .3086". Two post-'64 hammer forged 308 Win barrels were also .3086"; one a 1976 Palma match and the other a 1974 regular commercial match version.

Only bullets that tested sub MOA in all was Lapua D46 185-grain FMJRB match bullets .3092" diameter and WCC 197-grain BTHP match bullets at .3088" diameter.
 
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Unclenick

Staff
That would not have been an example of a tight Palma bore.;) I had in mind the custom barrels like Krieger's .30 Tight series.
 
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