223 vs 5.56 Pressures

Unclenick :

I don't remember ever reading any info about the velocities SAAMI gets while doing there test . I assume they have this data . Is it ever published or otherwise accessible on there website ?

Does SAAMI even care if there test barrels are 20" or 30" ? I believe most peak pressures are earlier in the combustion process rather then lets say 24" down the barrel . I get that there would be a minimum length that all barrels would likely need to be but as far as SAAMI goes . Does it really matter if the test barrel is 20" or 30" ( speaking generally here ) I'm sure there are some exceptions .
 
I asked this of Hornady the other day.

I noticed that your 223 and your 5.56 55gr GMX ammo are identical as far as performance.
Do you test these two rounds in the same chamber/test barrel or do you have one for 223 and one for 5.56 with a longer throat?
When testing your 223 and 5.56 do you use the same MAP or do you have different pressure specs for the 223 compared to the 5.56?
Thanks
Merry Christmas

This is Hornady's Reply.

Mr. xxxxx
Thanks for contacting us. We absolutely have a designated 5.56 NATO chamber pressure barrel that is used for Pressure and Velocity testing. The MAP for 223 is 55K psi and the MAP for the 5.56 NATO is 60k psi, however we typically use a MAP of 57,500 for our NATO rounds. Thanks again,



From: Hornady Manufacturing, Inc [mailto:webmaster@hornady.com]
Sent: Wednesday, December 23, 2015 9:24 PM
To: tech <tech@hornady.com>
Subject: "Technical Inquiries" Contact from Steve xxxx
 
Steve :

Thanks for the link :)

Did Hornady say what there MAP was for there 223 . I see they drop the 5.56 by 2500psi . Would it be safe to assume they do the same with the 223 resulting in the 223 MAP being 52,500psi ? or do they up it to match the NATO loads ??

The other thing I'd like to be clear on is that it appears SAMMI uses the same 15" length barrel for all there testing regardless of cartridge or caliber . Yet they're showing velocities that would be from much longer barrels in there respective cartridges . I think I'm getting a little over my pay grade here so can someone explain how they are getting that velocity data from a 15" barrel ??
 
^^^^

Mr. xxxxx
Thanks for contacting us. We absolutely have a designated 5.56 NATO chamber pressure barrel that is used for Pressure and Velocity testing. The MAP for 223 is 55K psi and the MAP for the 5.56 NATO is 60k psi, however we typically use a MAP of 57,500 for our NATO rounds. Thanks again,

This is all they said, they did not indicate if the 223 was reduced below 55K psi.
 
I have a case of Malaysian surplus 5.56 ammo 55 gr that chronographs at 3300 fps with a 14" barrel.

Somebody missed the boat with pressure with that ammo.

The guy that gave me the case 20 years ago was afraid it was too hot to run through his AR15.
 
^^^
That's s good point, the AR-15.

What is the recommended Max pressure allowed for this rifle design?

The 223, 6.5 Grendel, 300 Blackout, 6.8 SPC and the 30 AR all have a SAAMI Max at or below 55K psi.

If 55K is the Max, how is it that this lone wolf, the 5.56 can run safely in an AR-15 at 62K?
 
attachment.php

This 35 gr Vmax and Blue Dot at 4200 fps will not cycle my AR15.

The event is too fast. No amount of Blue Dot and 35 gr will cycle my AR15. Less powder lowers the gas pressure. More powder shortens the event.

What does it all mean?

The ammo pressure for best for typical AR15 operation, is lower for heavier bullets and higher for lighter bullets.

The ammo pressure for best for typical AR15 operation, is lower for slower powders and higher for faster powders.

Maybe you can adjust AR15s. I have not. I sure have adjusted BARs and FALs.
 
Clark, your pic above is one of the better examples -- save in extreme cases -- of why I no long look at primer
condition for pressure indicators. (Round edges still evident; and while there is cratering, that can be also
be caused by oversize firing pin hole)

Brass flow, on the other hand is irrefutable:eek:; followed by primer pocket expansion over repetitive firings.
 
Identical pressures, only if they are tested in the same chamber.
Click to expand...

It is possible to get different pressures from the same chamber. I do it every time I decide to cut down on case travel.

F. Guffey
 
The other thing I'd like to be clear on is that it appears SAMMI uses the same 15" length barrel for all there testing regardless of cartridge or caliber . Yet they're showing velocities that would be from much longer barrels in there respective cartridges . I think I'm getting a little over my pay grade here so can someone explain how they are getting that velocity data from a 15" barrel ??
Click to expand...

Metal God:
The usual PV barrel is 24 inches.
Are you misinterpreting the chart steve linked? It says "Velocity (fps) Nominal Mean Instrumental @ 15' Test Barrel"
That means the velocity reading is taken at 15 feet, not that the test barrel is 15 inches (or feet) long.
 
Jim :

Yes I did misread/interpret that . Thanks for the clarification . :) And I have to say I'm a little disappointed in my self there . It clearly says "Instrumental" and 15' not 15" :o
 
Clark, your pic above is one of the better examples -- save in extreme cases -- of why I no long look at primer
condition for pressure indicators. (Round edges still evident; and while there is catering, that can be also
be caused by oversize firing pin hole)
Click to expand...

Brass flow, on the other hand is irrefutable ; followed by primer pocket expansion over repetitive firings.
Click to expand...

Mehavey, is it possible you missed out on the case head expansion in the beginning. Before the Internet reloaders used factory ammo when deterring case head expansion. A good number for case head expansion in the big inning was .00025”. Then there were shell holders no one remembers, some of them fit. Again, before the Internet Herter sold flash hole gages. I have flash hole gages.

To make it work I am required to measure before firing and again after firing. Nothing different when determining case head expansion, to get past measuring case head expansion a reloader has to get past those that say it can’t be done.

Then there was the reloader that discovered .0005” case head expansion was too much; case head expansion when before the Internet .0005” was twice the daily recommended allowance.

F. Guffey
 
That has to have some other explanation. Board member Slamfire detailed a Navy test of 7.62 ammunition that got the pressure to increase around 50% by artificially aging it in heat. This can cause the deterrent coatings to break down before the nitrocellulose and nitroglycerin do, leaving you with a faster powder burn rate than it originally had. If the 5.56 ammo you saw used was surplus, be aware that exceeding military storage life limits is one reason for making it surplus. That doesn't automatically mean its bad, but the possibility exists. I had some very hot Portuguese 7.62 surplus at one time.

Another thing that can happen is just a factory loading error. Someone who'd done extensive testing for government agency ammunition procurement commented on another forum that when you fire many tens of thousands of rounds of commercial ammunition, eventually you see examples of every kind of error a handloader might make, including over and under loading, plus a few errors you never see reloading, like cases without flashholes or seated bullet jackets with no lead core.

My AR match rifle was built by Compass Lake, and Frank White's reamers are very close to a 223 reamer. They have an extra half thousandth of width at the base for feed reliability, but the freebore is actually about that much narrower than standard and is the same length as a 223. So, no significant difference. That rifle digests 5.56 ball ammo just fine. So something odd happened.

Regarding jamming the lands with a bullet, I've seen more pressure difference than MetalGod. About 20%. There's a pressure plot of this on RSI's web site. But the low end of the proof pressure range is about 133% pressure, so that should not cause the kind of symptom
Click to expand...

I never pursued it further to determine a root cause because switching ammo for the bolt action 223 resolved the issue. Whatever the exact cause was, the symptom was clearly too much pressure, as evidenced by bolt lockup and case inspection afterwards, this was a long time ago, the 5.56 ammo was genuine M855 (not XM855), The rest of the case of M855 was eventually fired through an AR-15 without issues. I have a hard time not accepting manufacturers warnings to this day.
 
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