223 vs 5.56 Pressures

S

steve4102

New member
I Know not again, but.

In checking out some 223 and 5.56 ammo at Midway, I found that most American made 223 ammo has the same FPS and ballistics as it's 5.56 brother.

An example would be Winchester WB 55gr FMJ in 223 and 5.56.
http://www.midwayusa.com/product/29...tion-223-remington-55-grain-full-metal-jacket

http://www.midwayusa.com/product/29...3131-556x45mm-nato-55-grain-full-metal-jacket

Both are loaded with the same bullet, both have identical ballistic properties.

5.56

Technical Information
Caliber: 5.56x45 (223 Remington)
Bullet Weight: 55 Grain
Bullet Style: Full Metal Jacket
Case Type: Brass

Ballistics Information:
Muzzle Velocity: 3240 fps
Muzzle Energy: 1282 ft. lbs.


223

Technical Information
Caliber: 223 Remington
Bullet Weight: 55 Grain
Bullet Style: Full Metal Jacket
Case Type: Brass

Ballistics Information:
Muzzle Velocity: 3240 fps
Muzzle Energy: 1282 ft. lbs

The fact that these two rounds that have identical components and also have identical performance would indicate that the rounds themselves were also Identical, correct?

Or are they?

We all know the 5.56 chamber has a longer throat. Shooting identical ammo in a 223 chamber will generate slightly higher pressure than in a 5.56 chamber.

My question, are these factory rounds actually Identical, or does Winchester and others use different test barrels, one in 223 and one in 5.56 with the longer throat?

If the barrels are identical, then there is no difference between 5.56 and 223 in these American manufactured ammo, correct.

If the barrels are different, one in 223 and one in 5.56 then, what are the odds that they would come up with identical FPS at same pressures?
 
Not sure if there are any case size differences but from what I can tell for .223 that is a hot/near max load and "Normal" for 5.56 NATO although there is not much if any load data for the 5.56 that is much higher if at all.

So if you were to look at just the pressure it would be on the higher end for .223 and normal for 5.56.
 
SAAMI Std 223 and CIP Std 5.56 are effectively the same,
The pressure measurements are taken at different points,
and therefore not apples-to-apples
 
The longer throat and longer minimum headspace in the 5.56 are about full auto reliability with a range of specialty ammo. The pressure difference due to the chamber differences are all well under SAAMI lot variation allowances. The cases have identical exterior dimensions.

The test barrels probably reflect the differences, but will be their respective minimums. The military also includes a gas port pressure range that has to be met and they allow less velocity variation for a given bullet weight than SAAMI. As a result, military ammo is usually kept a little more carefully near the rating maximums than commercial ammo is.
 
Thanks.

Maybe I didn't phrase my question correctly. Let me try again.

The two rounds I linked have Identical components and Identical velocities from the same American manufacturer (Win). To me that means that they also have Identical pressures.

Identical pressures, only if they are tested in the same chamber.

Are these loads both tested in the same chamber or do Federal, Hornady, Winchester, etc. actually have both testing chambers, one in 5.56 with a longer throat and one in 223 with a SAAMI throat?

If they are tested in different chambers then my theory that these two rounds are Identical is in error, yes?
 
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Going out on a limb, the lab would use the same pressure/test barrel set-up for both cartridges.

UncleNick has already explained how two identical ballistic cartridges would measure two different
pressures in the SAAMI/CIP world HERE.
 
Thanks and yes I have read UncleNick's postings.

I am aware that different testing methods would result in identical rounds reading differently.

My question is about Identical testing methods used in different sized chambers?

Going out on a limb, the lab would use the same pressure/test barrel set-up for both cartridges.
Click to expand...

That is where I am leaning as well, but that brings up another question, why.

Why package one marked 223 and one marked 5.56 if there is absolutely zero difference?
 
Some brands may be the same thing, but I can assure you, some brands of ammunition definitely have a difference between 223 and 5.56 NATO, If you don't think so then disassemble a couple and see for yourself. The ammo may be very similar, but .223 ammunition was probably worked up and tested in a 223 chamber, 5.56 ammunition was probably done in a 5.56 chambered barrel.

I can tell you first hand that the warnings about firing 5.56 ammo in a .223 chambered rifle are valid, it is certainly possible to have dangerously high pressure depending on the rifle/chamber.
 
I can tell you first hand that the warnings about firing 5.56 ammo in a .223 chambered rifle are valid, it is certainly possible to have dangerously high pressure depending on the rifle/chamber.
Click to expand...
iraiam, please expound on this. I would like to hear what happened to make you say this.
 
iraiam said:
I can tell you first hand that the warnings about firing 5.56 ammo in a .223 chambered rifle are valid, it is certainly possible to have dangerously high pressure depending on the rifle/chamber.
Click to expand...

I believe that to be a myth based on people looking at the SAAMI (and now, under SCATP 5.56, U.S. Military) 55,000 psi limits and the NATO and CIP 62,366 psi limit and at the older 52,000 CUP military number that was reported in tech manuals as psi, and not understanding that, despite the numbers, these were actually all the same absolute pressure. Even if they weren't, the NATO/CIP number is only 13.4% higher than the SAAMI number. By comparison, the SAAMI proof range peaks at about 40% higher than SAAMI MAP, so no kind of disaster could result even if the pressure difference were real and not just an instrumentation artifact. Indeed, SAAMI Maximum Extreme variation allows, in an improbably worst case, for individual rounds in a lot to be up to about 18% over MAP and CIP allows 15% over MAP, so the 13.4% difference is smaller than that. If the pressure differences were real and the worst case over MAP round were fired in the lower pressure chamber, it would still be at the low end of the proof range and no catastrophic failure would occur.

Under SCATP 5.56 and SCATP 7.62, the U.S. military has adopted the same conformal pressure transducer that SAAMI has standardized on. I presume the chambers cut into them are military, though, and that if Winchester produces 5.56 on contract for the military, that they own test guns with the military spec chamber. The difference in pressure between a SAAMI minimum chamber and a 5.56 minimum chamber is smaller than the difference between a SAAMI minimum and a SAAMI maximum field reject chamber, so, again, I don't see where a huge difference would come from.

Keep in mind that Remington adopted the .223 Remington as a civilian version of the 5.56 round. They really did start out the same.
 
Why package one marked 223 and one marked 5.56 if there is absolutely zero difference?
Click to expand...
There are people that are " less knowledgeable " that will only use what is marked on their rifle. If it is only marketed as 1 of the 2 cartridges a huge portion of the market disappears. It is all about money.
 
It's not zero difference, it's just not a peak pressure difference or a geometry difference that is the issue. What makes them different is the cartridges labeled 5.56 are supposed to conform the the NATO compatibility standards. There are two symbols associated with them. One is for firing compatibility and the other is combined with it to indicate ballistic compatibility. That is, cartridges with the first symbol will function in all NATO small arms and machine guns, while those also bearing the second symbol will meet ballistic standard as to range and trajectory and accuracy. These symbols are:

NATO%20compatibility_zpsnlb7lru5.gif


To meet the functional compatibility standard, the peak pressure limit must not be exceeded and a gas port pressure window has to be met. To meet the ballistic compatibility standard, bullet weight and ballistic coefficients have to fall within specified limits and muzzle velocity from a standard length test barrel has to be within a velocity window.

The same is true with .308 Winchester and 7.62 NATO.

It is not uncommon for commercial ammo to feel weaker. This is because SAAMI has a wider velocity window for the same bullet weight and no gas port pressure specification. As a result, commercial ammo can be and often is loaded down a bit for economic reasons, such as what powder happened to be in stock at the time that could be used in the loaded round and other rounds. If the military gets powder that's too far off to produce required ballistics, the gas port pressure window, and stay inside the peak pressure limit, they just reject the whole lot for the particular round the load was being developed in and move on to another lot. Commercial loaders don't always have the same economic luxury.
 
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Unclenick, I have personally witnessed a factory M855 round fired in a bolt action rifle chambered in .223 develop enough pressure to lock the action up where it had to be beat open with a hardwood club sized dowel. The rifle is fine but only shoots .223 ammunition now without issue.

All this being said, I think it's likely that only a small percentage of chamber/ammo combinations will actually cause this. maybe the rifle in question has a tight chamber or a short leade to the rifling, but whatever the root cause, it did in fact happen. I can only assume, particularly after having this happen, that the warnings from firearm manufactures about this have some validity.
 
I doubt any ammo that was different would have the exact same MV in there test . What I don't see is the barrel lengths for each test barrel . I think it's likely if the 5.56 ammo was tested in a 5.56 chambered barrel . That barrel would be 20" or less . At the same time the 223 chambered barrel would likely be 22" or longer .

So in theory a lower pressure 223 round fired from a 24" barrel could have MV very close to a higher pressure 20" 5.56 barrel . Again though . IMHO no way they would have the exact same MV . I'd say the Midway data is incorrect at best .
 
...witnessed a factory M855 round fired in a bolt action rifle chambered in
.223 develop enough pressure to lock the action up where it had to be
beat open with a hardwood club sized dowel.
Click to expand...
That's in excess of 80-85,000psi for brass to flow that badly.
I suspect something else was afoot, not simply 5.56/223.

As UncleNick points out, pressure-wise the two ammo types are
similar if not the same. The 223 chamber does have a shorter throat
than the 5.56, so jam-fit is possible with specific military bullet ogives.
But jam fit wouldn't account for more than several ksi (2-5) in most
instances.
 
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I doubt any ammo that was different would have the exact same MV in there test . What I don't see is the barrel lengths for each test barrel . I think it's likely if the 5.56 ammo was tested in a 5.56 chambered barrel . That barrel would be 20" or less . At the same time the 223 chambered barrel would likely be 22" or longer .

So in theory a lower pressure 223 round fired from a 24" barrel could have MV very close to a higher pressure 20" 5.56 barrel . Again though . IMHO no way they would have the exact same MV . I'd say the Midway data is incorrect at best .
Click to expand...

Hornady 223 and 5.56 ammo.

Hornady 223 55gr GMX Superformance

Test Barrel= 24 inches.

MV = 3275fps.

http://www.hornady.com/store/223-Rem-55-GR-GMX-Superformance/


Hornady 5.56 55gr GMX Superformance

Test Barrel= 20 inches

MV= 3130fps

http://www.hornady.com/store/5.56-NATO-55-GR-GMX-Superformance/

Using Quickload to calculate the velocity difference due to barrel length we come up with the above 223 load having a MV of 3147 fps out of a 20 inch barrel. That is about as identical as it gets, I think?


As for Midway, they list identical velocities as Hornady, 3275 for the 223 and 3130 for the 5.56.
 
Using Quickload to calculate the velocity difference due to barrel length we come up with the above 223 load having a MV of 3147 fps out of a 20 inch barrel. That is about as identical as it gets, I think?
Click to expand...

My point was that if that ammo was tested in the proper chambered barrels . The barrels would not likely be the same length . Therefore if the ammo was in fact identical there velocities would not be the same .

On the other hand a lower pressured round out of a longer barrel "may" produce similar velocities as a higher pressure round from a shorter barrel .

As you showed the rounds can be close but the exact same IMO is not likely . That said we are talking about the actual manufacturer of the ammo and they very well could load the rounds to have the identical velocities . ;)
 
Steve,

Note that Hornady uses production firearms for their velocity testing, and not SAAMI standard test barrels. The SAAMI standard pressure/velocity barrel for .223 Remington is 24.000" ±0.010", as it is for all but the few rifle cartridges that have 20.000" ±0.010" test barrel lengths. Those are: .30 Carbine, 350 Remington Magnum, 351 Winchester, 44 Magnum rifle, and 7.62×39. All others have the 24" spec.

iraiam said:
Unclenick, I have personally witnessed a factory M855 round fired in a bolt action rifle chambered in .223 develop enough pressure to lock the action up where it had to be beat open with a hardwood club sized dowel. The rifle is fine but only shoots .223 ammunition now without issue.
Click to expand...

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 you described.
 
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