223 or 5.56mm : Difference?
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5.56 is the military designation for the .223. The difference is that 5.56 is loaded to operate at a pressure that exceeds SAAMI spec. Barrels that are chambered to fire 5.56 have chambers that differ a bit from standard .223 chambers. The major difference is in the throat dimensions. The 5.56 chamber has a longer throat. I really don't remember all of the other differences in specs. I wouldn't say that one has any pros or cons as far as .223 vs 5.56 goes except that most of the surplus type of ammunition that you will find is going to be 5.56 and most of the uber accurate commercial stuff is going to be loaded to .223 spec. I suppose that one pro of going with 5.56 ammo is that it's loaded hotter than its commercial counterparts. A downside of 5.56 ammo is that it's usually trash in terms of precision accuracy. It was never intended nor designed to be super accurate.
HorseSoldier
Member
Depends. Foreign surplus is totally a crap shoot. Domestic surplus -- M855 green tip is anywhere from a 1-4 MOA round, with big variation from lot to lot and even with lots, due to the complex construction and the steel penetrator. Mk 262 will match anything production ammo is capable of accuracy wise, and will typically exceed the capabilities of the rifle shooting it in terms of accuracy.
I can't agree with you on the Mk262 ammo. That ammo, as specified by the military, has a specific purpose and accuracy is not on the top of the list of requirements for that ammo, from what I understand. My handloads and even Federal Gold Medal Match shoots far more accurately than the Mk262 does, out of my rifles, although neither my loads nor the FGMM have nearly the velocity of the Mk262.
HorseSoldier
Member
Mk 262 was procured specifically to support the SPR program for sniping applications. It has since filtered out to support some DMR work as well.
Accuracy is the specific reason for its adoption.
PR-NJ
Member
From what I understand, you can shoot .223 Remington in a 5.56 NATO rifle, but generally, you shouldn't try the other way around.
Interestly, it's the converse for a larger caliber. You can shoot NATO 7.62x51 in a .308 Win rifle, but generally, you shouldn't do the opposite.
In very simple (and technically incorrect) terms, MOA, "minute of angle," is a measure of shooting precision sometimes (and again, incorrectly) meant to mean within an inch at 100 yards.
Interestly, it's the converse for a larger caliber. You can shoot NATO 7.62x51 in a .308 Win rifle, but generally, you shouldn't do the opposite.
In very simple (and technically incorrect) terms, MOA, "minute of angle," is a measure of shooting precision sometimes (and again, incorrectly) meant to mean within an inch at 100 yards.
ArmedLiberal
Member
Has anyone heard of a rifle marked .223 blowing up from the use of 5.56? It's not clear to me how important this difference is.
Clearly if your rifle barrel is rated for 5.56, you can do no harm using .223 ammo.
http://en.wikipedia.org/wiki/5.56x45mm_NATO
5.56mm NATO versus .223 Remington
The 5.56 mm NATO and .223 Remington cartridges and chamberings are similar but not identical. Military cases are generally made from thicker brass than commercial cases; this reduces the powder capacity (an important consideration for handloaders), and the NATO specification allows a higher chamber pressure....
...This means the NATO maximum service pressure of 430 MPa (62,366 psi) for 5.56 mm NATO, is reduced by SAAMI to 379.21 MPa (55,000 psi) for .223 Remington. In contrast to SAAMI, the other main civil standards organization C.I.P. defines the maximum service and proof test pressures of the .223 Remington cartridge equal to the 5.56 mm NATO....
The 5.56 mm NATO chambering, known as a NATO or mil-spec chamber, has a longer leade, which is the distance between the mouth of the cartridge and the point at which the rifling engages the bullet. The .223 Remington chambering, known as SAAMI chamber, is allowed to have a shorter leade, and is only required to be proof tested to the lower SAAMI chamber pressure. To address these issues, various proprietary chambers exist, such as the Wylde chamber (Rock River Arms)[14] or the ArmaLite chamber, which are designed to handle both 5.56 mm NATO and .223 Remington equally well. The dimensions and leade of the .223 Remington minimum C.I.P. chamber also differ from the 5.56 mm NATO chamber specification.
Using commercial .223 Remington cartridges in a 5.56 mm NATO chambered rifle should work reliably, but generally will not be as accurate as when fired from a .223 Remington chambered gun due to the longer leade. Using 5.56 mm NATO mil-spec cartridges (such as the M855) in a .223 Remington chambered rifle can lead to excessive wear and stress on the rifle and even be unsafe, and SAAMI recommends against the practice. Some commercial rifles marked as ".223 Remington" are in fact suited for 5.56 mm NATO, such as many commercial AR-15 variants and the Ruger Mini-14 (marked ".223 cal"), but the manufacturer should always be consulted to verify that this is acceptable before attempting it, and signs of excessive pressure (such as flattening or gas staining of the primers) should be looked for in the initial testing with 5.56 mm NATO ammunition.
It should also be noted that the upper receiver (to which the barrel with its chamber are attached) and the lower receiver are entirely separate parts in AR-15 style rifles. If the lower receiver has either .223 or 5.56 stamped on it, it does not guarantee the upper assembly is rated for the same caliber, because the upper and the lower receiver in same rifle can, and frequently do, come from different manufacturers - particularly with rifles sold to civilians or second-hand rifles.
In more practical terms, as of 2010 most AR-15 parts suppliers engineer their complete upper assemblies (not to be confused with stripped uppers where the barrel is not included) to support both calibers in order to protect their customers from injuries and to protect their businesses from litigation following the said injuries.
Clearly if your rifle barrel is rated for 5.56, you can do no harm using .223 ammo.
http://en.wikipedia.org/wiki/5.56x45mm_NATO
5.56mm NATO versus .223 Remington
The 5.56 mm NATO and .223 Remington cartridges and chamberings are similar but not identical. Military cases are generally made from thicker brass than commercial cases; this reduces the powder capacity (an important consideration for handloaders), and the NATO specification allows a higher chamber pressure....
...This means the NATO maximum service pressure of 430 MPa (62,366 psi) for 5.56 mm NATO, is reduced by SAAMI to 379.21 MPa (55,000 psi) for .223 Remington. In contrast to SAAMI, the other main civil standards organization C.I.P. defines the maximum service and proof test pressures of the .223 Remington cartridge equal to the 5.56 mm NATO....
The 5.56 mm NATO chambering, known as a NATO or mil-spec chamber, has a longer leade, which is the distance between the mouth of the cartridge and the point at which the rifling engages the bullet. The .223 Remington chambering, known as SAAMI chamber, is allowed to have a shorter leade, and is only required to be proof tested to the lower SAAMI chamber pressure. To address these issues, various proprietary chambers exist, such as the Wylde chamber (Rock River Arms)[14] or the ArmaLite chamber, which are designed to handle both 5.56 mm NATO and .223 Remington equally well. The dimensions and leade of the .223 Remington minimum C.I.P. chamber also differ from the 5.56 mm NATO chamber specification.
Using commercial .223 Remington cartridges in a 5.56 mm NATO chambered rifle should work reliably, but generally will not be as accurate as when fired from a .223 Remington chambered gun due to the longer leade. Using 5.56 mm NATO mil-spec cartridges (such as the M855) in a .223 Remington chambered rifle can lead to excessive wear and stress on the rifle and even be unsafe, and SAAMI recommends against the practice. Some commercial rifles marked as ".223 Remington" are in fact suited for 5.56 mm NATO, such as many commercial AR-15 variants and the Ruger Mini-14 (marked ".223 cal"), but the manufacturer should always be consulted to verify that this is acceptable before attempting it, and signs of excessive pressure (such as flattening or gas staining of the primers) should be looked for in the initial testing with 5.56 mm NATO ammunition.
It should also be noted that the upper receiver (to which the barrel with its chamber are attached) and the lower receiver are entirely separate parts in AR-15 style rifles. If the lower receiver has either .223 or 5.56 stamped on it, it does not guarantee the upper assembly is rated for the same caliber, because the upper and the lower receiver in same rifle can, and frequently do, come from different manufacturers - particularly with rifles sold to civilians or second-hand rifles.
In more practical terms, as of 2010 most AR-15 parts suppliers engineer their complete upper assemblies (not to be confused with stripped uppers where the barrel is not included) to support both calibers in order to protect their customers from injuries and to protect their businesses from litigation following the said injuries.
benEzra
Moderator Emeritus
"Has anyone heard of a rifle marked .223 blowing up from the use of 5.56? It's not clear to me how important this difference is."
I have 'heard' of it, but that's about the closest I've come. When I got my first gun chambered in 5.56, I was trying to do some research as to the difference of 5.56 and .223 ammo. This seemed to be the main thing that people said could happen if you shot 5.56 in a .223 gun.
From what it seems though, I guess the most popular rifles (such as the AR-15s) are all 5.56, so this issue would not apply if you're shooting one of those
I have 'heard' of it, but that's about the closest I've come. When I got my first gun chambered in 5.56, I was trying to do some research as to the difference of 5.56 and .223 ammo. This seemed to be the main thing that people said could happen if you shot 5.56 in a .223 gun.
From what it seems though, I guess the most popular rifles (such as the AR-15s) are all 5.56, so this issue would not apply if you're shooting one of those
Maverick223
Member
5.56NATO is generally cheaper, so stock up on good 'ole mil-surp 55gr. FMJ for all your plinkin' needs. OTOH, commercial .223Rem. affords better bullets, so it is more useful for come tasks if you don't handload. I use mostly 5.56NATO (or my handloaded equivalent) for training and target use, and commercial bullets loads with ballistic tips, HPs, or SP bullets for defensive and varmint use.
Maverick223
Member
Yep, no problems with the Wylde chamber...in fact it preserves accuracy (by having a bit tighter chamber), whilst allowing you to shoot 5.56NATO as well (by having a longer throat). It is the best of both worlds (though reliability is ever so slightly less due to the tighter chamber).
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