The 5.56 / .223 pressure discussion
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Old 07-30-2013, 03:54 PM   #1
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Default The 5.56 / .223 pressure discussion

I know we have all been down this road a time or 2 and it always comes up as 5.56 has higher pressure than the .223 and hotter charge than the .223 . I have done some searching on this as I find it kind of hard to believe since the velocity is really pretty equivalent between the 2 using the same grain bullet . From what I have read and I printed all these doncuments and have gone thru them several times to recheck myself . I think what people are seeing as pressure differences in specs are complete different types of pressure measurements . Such as the SAAMI rating , EPVAT rating , SCATP5.56 rating and the CIP ratings .
Heres what I dont get . I have copied and pasted this for reference


Quote:
The US military defines test procedures for 5.56mm NATO in SCATP 5.56, and 7.62mm NATO in SCATP 7.62.[9] These procedures are based on the SAAMI test methodology.

NATO, however, defines 5.56mm, 7.62mm, 9mm and 12.7mm using the NATO EPVAT test methods, which includes pressure testing that generally conforms to C.I.P. pressure test methods instead. For the 9mm NATO EPVAT specifies that for 9×19mm Parabellum (9mm Luger in C.I.P. nomenclature and 9mm NATO in NATO nomenclature), the transducer must be positioned at the mid case position (9.5 millimetres (0.37 in)) from the breech face instead of C.I.P.'s 12.5 millimetres (0.49 in) from the breech face. For NATO EPVAT testing of military firearms ammunition NATO design EPVAT test barrels with Kistler 6215 channel sensor transducers are used.
Yet the EPVAT maximum pressure rating on the 5.56X45 cartridge is 62,366 psi or 430.00MPa and the CIP maximum pressure for the .223 is 62,366 psi or 430.00 MPa .
I know that the specs for the 5.56 brass are basically the same with the exception of the radius on the neck on the 5.56 its squared off on the .223 its radiused 2,54 at the neck and ,64 on the shoulder .
Im just wondering how much more pressure there really is shooting 5.56 in a .223 chamber with the different radius on the cartridge .

Much more research led me to this link http://www.luckygunner.com/labs/5-56-vs-223/#bookmark4
which was very interesting and led me to believe that there are increased pressure because of the tighter tolerances of the .223 over the 5.56 , not the fact that the 5.56 is a hotter cartridge than the .223 .
In reality is your rifle going to blow up , very highly unlikely . Is it harder , more wear and tear on your rifle ? Not really . Is it really unsafe to fire 5.56 in your .223 chamber ? Thats a answer you have to ask your self .
Have I done it ? Yes. Is there a noticeable difference to me ? No . Chronograph differences were so minor it could very between different cartridges of the same ammo . Most differences were less than 25 fps even with the same brand cartridges I used . This shows me that factory ammo #1 isnt real consistent and #2 will NEVER be as accurate and the guy loading precision reloads .


In a SHTF scenerio , I would put either thru it without second guessing myself on it . IMO your going to get better accuracy our of the tighter tolerances of the .223 than you are a 5.56 round


5.56 on the top , .223 on the bottom
800px-5.56x45mm_nato.jpg   800px-.223_remington.jpg  
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Old 07-30-2013, 04:23 PM   #2
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The difference isnt in typical fmj rounds. Its when you start using specialized ammo like tracers and ap rounds like the ss109 and its descendants. The shorter lead combined with tighter throat and chamber on the 223 will cause a big pressure spike because the bullet can and does in some configurations contact the lands and grooves.

Pressure isnt a one to one correlation with speed of the bullet.

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Old 07-30-2013, 04:34 PM   #3
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Originally Posted by JonM View Post
The difference isnt in typical fmj rounds. Its when you start using specialized ammo like tracers and ap rounds like the ss109 and its descendants. The shorter lead combined with tighter throat and chamber on the 223 will cause a big pressure spike because the bullet can and does in some configurations contact the lands and grooves.

Pressure isnt a one to one correlation with speed of the bullet.
Sorry I was referencing a 62 gr bullet between the 2 . But yes the more weight are going to mean higher spikes for sure whether its a 5.56 or .223 chamber. You always see on other forums , people talking about how the 5.56 cartridge is hotter . Its the I-net say it isnt so
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Old 07-30-2013, 05:49 PM   #4
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Interesting. Learn something everyday.

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Old 07-30-2013, 09:36 PM   #5
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I was always told over the years they were the same so I have always shot either one in my Colt SP1. I did not know until I started going on forums that they were not supposed to be interchanged. I have shot hundreds of rounds through my Colt of both .223 and 5.56 with no problems using the 55gr fmj. Have also had friends shooting AR's that shot the same ammo as me and they never had any problems. Now I'm not saying this is the right thing to do,just saying I never had any or know of any problems from my personal experience.

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Old 07-30-2013, 09:58 PM   #6
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I was always told over the years they were the same so I have always shot either one in my Colt SP1. I did not know until I started going on forums that they were not supposed to be interchanged. I have shot hundreds of rounds through my Colt of both .223 and 5.56 with no problems using the 55gr fmj. Have also had friends shooting AR's that shot the same ammo as me and they never had any problems. Now I'm not saying this is the right thing to do,just saying I never had any or know of any problems from my personal experience.
your not going to see any difference in a 55grain fmj. its things like surplus ss109 tracers and other special use cartridges.

bullets for the 556 has a larger allowance in how far the ogive can be down the body of the bullet at its widest point which in the diagram is the S measurement. due to the need to keep the same weight when your putting in a phosphorous charge or a steel penetrator the displaced lead has to be moved further up in the bullet body making that S measurement further out.

the reason folks say dont use 556 in a 223 is because we have no idea what ammo your using where it came from and if it was made to a lesser standard. some countries use a lead alloy or a steel jacket or some other funky stuff which can make the S measurement safe for a 556 but not for a 223
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Old 07-30-2013, 10:35 PM   #7
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So JonM are you saying as long as I am shooting the standard 55gr FMJ I should be ok? That's what I have always shot in it because from what I have been told that the old sp1 has the 1in 12 twist in the barrel and that's what it was made to shoot the best. I'm not a target shooter or anything I just want it to go bang when it pull the trigger but don't want it to blow up in my face either. I'm in the process of building another AR now, I have the lower finished just trying to save enough money to start the upper. Will be a little more selective in ammo for it.

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Old 07-30-2013, 10:44 PM   #8
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Another wrinkle:

I have always heard ( but dont know if its true but it was plausible to me) that the 5.56mm rounds have stronger casings and/or better/more sealant to meet milspec longevity.

Among other things, this would explain why a PMC Xtac 55gr (5.56) round generally costs 15-20% more than a PMC Bronze (223) round.

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Old 07-31-2013, 04:00 AM   #9
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Another wrinkle:

I have always heard ( but dont know if its true but it was plausible to me) that the 5.56mm rounds have stronger casings and/or better/more sealant to meet milspec longevity.

Among other things, this would explain why a PMC Xtac 55gr (5.56) round generally costs 15-20% more than a PMC Bronze (223) round.

This is absolutely not true. I've weighed Lake City surplus brass and it typically weighs less than most commercial brass. Sellier and Bellot .223always seem to weigh the most. Let's remember the government is buying stuff from the lowest bidder
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Old 07-31-2013, 02:12 PM   #10
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Quote:
Originally Posted by michael a View Post
So JonM are you saying as long as I am shooting the standard 55gr FMJ I should be ok? That's what I have always shot in it because from what I have been told that the old sp1 has the 1in 12 twist in the barrel and that's what it was made to shoot the best. I'm not a target shooter or anything I just want it to go bang when it pull the trigger but don't want it to blow up in my face either. I'm in the process of building another AR now, I have the lower finished just trying to save enough money to start the upper. Will be a little more selective in ammo for it.
Long as your not buying wolf or other surplus cheap 55grain shouldnt have an issue. Sticking with things like major brand ammo there isnt a lick of difference.

If your concerned get a hornady oal gage, bullet comparator for .224, modified 223 case. You will need some way to pull a bullet safely from a loaded cartridge such as a kinetic bullet puller, they are pretty cheap can be had around 9$ or so, and some calipers for measuring.

Measure your chamber depth it will give the distance to the lands then the comparator can measure the distance to the ogive on loaded ammo. Loaded ammo shorter than your chamber depth your good to go.

I personally wouldnt run factory 556 in a 223 unless your measuring each batch
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