.223 Rem vs. 5.56 NATO Chambers/Overpressure Issues?

[Unclenick]

Originally Posted by JeepHammer

In 2012, according to the government,
Governmental and Military went to Exactly the same case as 'Civilian' .223 Rem.

That's odd. That would make them heavier. Lake City 5.56 cases have generally as light or lighter than civilian cases since well before 2012. Look at the LC 06 in this article. 92 grains. Lightest cases among all measured, including a number of commercial brands.

Are you sure your source wasn't referring to 7.62 NATO? Those military cases really are heavier than commercial by as much as about 6%. When Federal developed the Mk316 mod.0 sniper ammo for the M24 sniper system, they used their own brass standards to get better accuracy. Lack of failures there may have prompted a change in military thinking.

Regarding the .223/5.56 pressure. Back when the copper crusher was king and M193 was the standard ball ammo, the pressure standards were:

M193/223 Rem
Military: 52,000 psi by copper crusher.
SAAMI: 52,000 CUP (same as psi by copper crusher, above)
Euro NATO: 3700 bar (53,664 psi) by copper crusher
CIP: 3700 bar (53,664 psi) by copper crusher

The slight difference in the NATO pressure will be due to their slightly different crusher geometry, rounding error, and possibly just normal variation in the mean value due to the fact copper crushers are not very precise instruments in the first place.

So, all through the Vietnam war and on through to the 80's, at least, the 5.56 and 223 pressures were all the same except for specialty ammo. M995 AP, for example, had a MAP (Maximum Average {peak} Pressure) of 50,250 psi.

And then the piezoelectric transducers came in and all that (relatively) uniform simplicity goes to pot.

First, our military started playing with transducers. Something went wrong with the equipment types. If you look at the specifications for M855 ammo you find it limits pressure to 55,000 psi, with three standard deviations not to exceed 61,000 psi. Reading copies of SCATO 5.56 for the time, the measurement is made using a "government approved pressure transducer". At the time they were experimenting with conformal transducers like the ones SAAMI uses. Since SAAMI adopted that same 55,000 psi value for their conformal pressure transducers, this seems likely. Today the military is using the Kistler 4206 transducers, same as Metric NATO and the later (2001 and on) documents describe that and have higher pressure limits. SAAMI, however, did not change.

And the metric folk across the pond took the reference ammo from the copper crusher days and tested it using those same Kistler transducers, NATO measuring at the case mouth and CIP at 25 mm (0.98") forward of the breech. Both came up with a standard of 430 MPa or 4300 bar. This converts to 62,366 psi. Today, that is the NATO pressure limit for 5.56 NATO, and it is the CIP limit for 223 Remington.

If you've been paying attention, you'll note that if you buy European 223 Remington ammunition, you are buying ammunition loaded with a 62,366 psi pressure limit by their measuring method. Norma, Lapua, Sellier & Bellot, Fiocchi, etc., and the Russian Wolf and Tulammo, as well. If you really think the nominally higher pressure limit of 5.56 NATO can harm your gun, stay away from foreign ammo. But before you let that scare you, look at your gun carefully. If the same basic action is made in .308 with the same barrel contour, you know that higher pressure with those thinner chamber walls and with the greater head cross-sectional area putting more thrust on the bolt face per psi is not going to damage the gun, so why should the same pressure in the smaller 223 case do it?

A note on test methods: with a little searching you will find things like the location of the pressure sample point at the case mouth or locating it mid-case results in about 2,000 psi difference in readings, worst case. Often there is almost no difference. There is a good measurement report on 223 vs. 5.56 mm in which Federal XM855 measures about 60,000 psi by strain gauge, and it is measured in two 5.56 chambers and one 223 chamber. The .223 chamber had the middle pressure value between the two 5.56 cases, so, again, the difference due to chambers is exaggerated. If you calculate the volume differences that the two chambers allow cases to expand to, you get very small percentage numbers. The more generous 5.56 chambers are really about ensuring smooth full-auto feed more than controlling pressure. The few specialty bullets that will make a significant difference in leade proximity are not commonly sold or used by civilians. The ball ammo shapes aren't particularly different from civilian shapes, including the bullet ogive. All the article authors trying to claim these factors I've just mentioned make big pressure differences are just searching for an explanation as to why the pressures are specified as different. I don't believe they are doing their homework on the differences in measuring systems.

As I've explained, the pressures weren't supposed to be different, originally. The different numbers were due to different pressure measuring methods at different points in history. Today, you can buy ammo loaded to a range of different pressures, apparently owing to some industry folk buying into the different numbers as real.

I am continuing to explore this topic a little further. I am putting another call into SAAMI, now that I have documented the military specs a little better, so see if they can add to the discussion.

[steve4102]

Looking forward to it Unclenick.

[JeepHammer]

Me Too!
I'm still confused...

The blurb I saw was a 10% weight reduction in 5.56, 7.62 & 50 Cal. ammo.
Didn't see a date for completion on that form. It was an internet copy, so I can't vouch for it's authenticity.

[Jimro]

I've got a theory that no one has proven wrong yet.

One of the problems that people don't like to talk about is the secondary pressure spike that comes from using too slow of a ball powder with too light of a projectile.

The 223 chamber exasperates the problem by having more initial resistance to the bullet meaning there is less effective volume for the secondary pressure spike. A looser lede or throat allows the bullet to be further down the bore when the secondary spike occurs, getting rid of the symptom caused by bad ammo.

People think that it's an ammo mismatch problem when it is in fact a bad ammo problem. By changing the chamber they are able to get rid of the high pressure symptoms and fall into a post hoc ergo propter hoc fallacy that it must be a chamber mismatch causing the pressure issues.

In fact the "popped primer" issue is almost always caused by a secondary pressure spike hitting when the bolt is unlocking or unlocked, allowing the brass to expand, cling to the walls of the chamber, and PUSH the primer out the back where it often falls into the trigger group. Then the pressure drops a bit, the brass springs back and shoots out under the residual pressure. If the pressure hit when the bolt was locked, you'd see pierced primers, not popped out primers.

Jimro

[Unclenick]

No doubt some issues occur with timing. A lot of domestic AR shooting, in particular, is with commercial ammo, some of which is loaded with very slow powder to meet the military velocity, but at the a lower peak pressure (part of the problem of buying into the numbers game). What is different is that the military tests not only peak pressure, but gas port pressure at a standard location and that has to be inside a tolerance range. The slow powders tend to have higher gas port pressure when used as I described, to there is a tendency for them to open the action fast. Additionally, when the same velocity is achieved by a slower powder than is usually used to achieve that velocity, the barrel time is longer, so that lengthens the gas impulse at that higher pressure. I'd have to examine how much, but it'll be something QuickLOAD can analyze well enough to proved some proportional result.

[Metal god]

The following has over max load data . DO NOT use !

Unclenick:
If you do run some numbers through Quickloads . Can you plug in 55gr FMJ BT , 26.5gr IMR 4320 , CCI #400 primer , COAL 2.240 . I'm getting about 2900fps from a 16" barrel and it feels hotter then other loads I use . It feels like I'm way over gassed and was thinking some of that had to do with the slower powder . I know I'm over max charge weight as well but It's my most accurate load with that powder by far .

[steve4102]

Originally Posted by Metal god

Unclenick:
If you do run some numbers through Quickloads . Can you plug in 55gr FMJ BT , 26.5gr IMR 4320 , CCI #400 primer , COAL 2.240 . I'm getting about 2900fps from a 16" barrel and it feels hotter then other loads I use . It feels like I'm way over gassed and was thinking some of that had to do with the slower powder . I know I'm over max charge weight as well but It's my most accurate load with that powder by far .

QL is more accurate if the exact case capacity of a fired case is plugged in.

The default capacity for the 223 in QL is 28.8gr H20. I have not found any case with Capacity that small.

My LC brass has a case capacity averaging 30.5gr H20.

If you could supply your case capacity of a fired case that would be extremely helpful.

Also the exact bullet , Brand is also important.

[Unclenick]

CAUTION: The following post includes loading data beyond or not covered by currently published maximums for this cartridge. USE AT YOUR OWN RISK. Neither the writer, The Firing Line, nor the staff of TFL assume any liability for any damage or injury resulting from use of this information.

Metal God,

My simple Excel file, based on Hodgdon's data for the 55 grain Speer Spire point, predicts 2902 fps from your barrel length (Hodgdon's is 24") and predicts 52,230 psi. Note that 26.5 grains is 0.4 grains over Hodgdon's maximum. Why there's is below the standard pressure limit, we don't know. It may be the powder gets squirrelly at higher pressures in this round.

QuickLOAD is in good agreement with the above when the case capacity is expanded from the default value to 29.4 grains. This is a low number. Most real cases seem to be closer to 30-30.5 grains case water overflow capacity.

I would suggest, if you are willing to go over published loads, that you should get the same velocity from 21.2 grains (21 grains is the listed maximum) of IMR 4198. It predicts a pressure of 49,761 CUP in the Excel file and very slightly lower psi in QuickLOAD than the 4320 load. It can do this because it burns much more completely in the short barrel. It fills the case to about 95%. It lowers the muzzle pressure about 10%, so gas port pressure will be down, too. It cuts 25% off your powder cost. Should be good to go, but work up toward it, just the same, for your lot of powder.

[mehavey]

Overpressure [short of brass extrusion] would show up as expanded primer pockets after a handful of reloads.
Barring evidence to that effect, 52ksi is certainly ballpark.

[Metal god]

Thanks UN

Most brass used is LC-11&12 mixed for that load . I have a large lot of that brass 600+ pieces that I cycle through . Problem with that is I use that brass for 2 other loads . I keep the brass separate per times loaded but not for each powder used . So no way to tell what powder was used last in a case . They all get placed into the same bin according to how many times they've been loaded .

The reason I went to 4320 was I wanted a powder that was not so commonly used . Over the last couple years I started to see that 4320 was available more then the more commonly used powders . I wanted at least one powder in my rotation that would be easier to get so that's why I use it . I normally would not even try that slow a powder with that light a bullet . In fact once I get more I'll be trying it with 62 & 69gr bullets to see how it does . On my burn rate chart 4198 is #70 and 4320 is #100 Not sure how accurate that is but anything close to that is a huge difference in my book .

[steve4102]

Originally Posted by mehavey

Overpressure [short of brass extrusion] would show up as expanded primer pockets after a handful of reloads.
Barring evidence to that effect, 52ksi is certainly ballpark.

How much over pressure?

The 223 has a SAAMI MAP of 55K psi. At what pressure would these loose pockets appear in the 223?

The 17 Remington has the same case head dimensions (.378), but it has a SAAMI MAP of 63K psi. At what psi would these loose pockets appear in the 17 Remington?

Would "overpressure" signs in the 223 appear just over 55K psi, but hold off with the 17 Remington until pressures exceeded 63K psi?

How does the brass case and the primers know what SAAMI has set for them and when they should show overpressure?

[mehavey]

Overpressure becomes brass/manufacturer-dependent at the top end -- even within the same
cartridge/chamber -- and some brass gives the ghost quicker that others. (e.g. soft Federal)

The failsafe/weaklink canary is the case itself, and here's my rules of thumb:

- Blown primers (all the way out): 20-25,000(+) psi too high [Immediate Stop]
- Ejector marks: 15-20,000 psi too high [Immediate Stop]
- Loose pockets after 2-3 firings: 8-10,000 psi too high [drop charge 5-6%+]
- Loose pockets after 5 firings: 3-6,000 psi too high [drop 2-4%]

[Clark]

steve4102
How does the brass case and the primers know what SAAMI has set for them and when they should show overpressure?

When I was 5 and standing in a lake, I could not figure out how the water knew there was air inside the inner tube. I was a poor kid and could not afford Archimedes' concept of density.

[mehavey]

steve4102
How does the brass case and the primers know what SAAMI has set for them and when they should show overpressure?

It's a refrigerator magnet puzzle rearrangement:

To wit:
"How does the SAAMI know what the brass case has is set for when they show overpressure"

ANS: See Post #37 above.

[Unclenick]

Originally Posted by Steve4102

The 223 has a SAAMI MAP of 55K psi. At what pressure would these loose pockets appear in the 223?

If cases were calibrated, there would be a fixed answer to that, But as recent posts about problems with the softness of Federal brass reveal, about the only thing the brass can tell you is when the pressure is too high for itself, as Mehavey described. Those numbers can be different not only within a lot of cases, but with some variation among the individual cases within the lot, as this Denton Bramwell article shows.

In general, I think if you measure the diameter of the head or the extractor groove, by the time it has expanded half a thousandth you are pretty definitely at higher pressure than that case is happy with, and you'd do best to back the load down 10% and work back up to, but don't exceed 5% less, checking again.

A more sensitive measure is the flash hole diameter. Mr. Guffey sent me a very handy tool for measuring this, but I don't know that he makes them any longer. If you get a 6/0 and a 5/0 taper pin, they cover the range of flash hole sizes, and you can measure how far they enter the flash hole to get and expansion indicator that way.

[Metal god]

Clark :

You've blown up a gun or two right . Any chance you have some pressure numbers or likely pressures you started seeing primers popping out , extractor marks etc ??

I personally have never pushed anything real hard to see how hot I can go . .5gr maybe 1gr over max . Reason is simple . I've almost always found an accurate load below max .

Steve :

I realized I did not give you the bullet type . I get them at the gun show from the large powder vendor . When I ask what they are they say , we think they are Winchester ( not kidding ) So I'll say they are Winchester 55gr FMJ-BT . FWIW . They appear to be the same as Hornady's 55gr bullet . But the Hornady's take .5gr less of some powders to be more accurate which leads me to think they are not Hornady bullets .

[JeepHammer]

Now you guys are cookin with gas! (Pun intended!)
Can't wait to get home and read it on a screen I don't need a magnifier for.

I'm with Metal God, my best accuracy usually come in under maximum,
If it doesn't it usually involves a poorly cut chamber and/or crown, or a 'Choke' in the rifling in my experence.

I was wondering, can someone run Win Small rifle primers, military cases, 26 grains Benchmark, and 55 grain Hornady V Max?
I'm not seeing overpressure and I'm finding good accuracy in AR & bolt rifles without overpressure signs... Except ONE AR that likes to leave primer rings...

[Clark]

Metal god
Clark :
.. you have some pressure numbers or likely pressures you started seeing primers popping out , extractor marks etc ??

I have over load work up in 19 Bagder, .223, .243, 25acp, 257 Roberts AI, 260, 270, 7mmRemMag, 32acp, 32sw, 32S&WLong, 32-20, 7.62x25mm, 7.62x39mm , 308, 7.62x54R, 8x57mm, .380, 9x19mm, 9x23mm, 357 Sig, 38 sp, 357 mag, 38sw, 40sw, 10mm, 10.4mm, 45acp, 45Colt, .410, and 45/70.
~ 10 years ago I asked another engineer [better at challenging Denton than me] who did Von Mises calculations for work and gun hobby if he would also do 223.
https://en.wikipedia.org/wiki/Von_Mises_yield_criterion
I was getting a good match with the QL prediction of pressure at the point where primer pockets failed, and his calculation. Not perfect.
I find the weakest to the strongest for pressure vs primer falling out:
*10mm
*25acp
*Mauser large Boxer
*Belted magnum
*223
-----------------
Then there are the cases so strong the primer pocket does not matter
*Mauser small Boxer
*rimmed cases in general [but not Norma 7x57 rimmed is as weak as good brands of 7x57 Mauser large Boxer]

My personal work up system in strong rifles is to work up until I find the threshold of extractor groove diameter change anywhere around the groove. This is not a loose primer pocket, but a much more repeatable threshold than loose primer pockets. Then I back off 4% for temp compensated powder and more like 6% for other powders, to find a usable load that I produce in quantity for myself.

If you look at my post last year, the 223 extractor groove starts to change between 80kpsi and 92kpsi. That does not mean the primer pocket will get loose. But it is a predictor of enough shots and it would:
http://thefiringline.com/forums/show...highlight=h335
That was in a Ruger #1 that has a breech face devoid of extractor or ejector cuts.


This is Blue Dot and 35 gr Vmax in one of my AR15s at 4200 fps.
It shows the extractor, ejector, and stretch marks.
The pressure has no meaning, the brass is destroyed. The same load will often produce 4100 fps and no change in the brass. Blue Dot is the wrong powder for high pressure in 223. It works best at 35kpsi. The 4200 fps load would not cycle an AR15 nor would any lessor load of that powder and bullet.

What does it all mean?
1) I want loads that are tuned to make my AR15s work.
2) I can take advantage of the large safety margins in 223 case head strength [compared to 55kpsi SAAMI] in my bolt and single shot 223s if I want to.

Chart below is Von Misses calcuations