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What is the difference between 223 and 5.56 in all the conversations I have had with the people I work with I have got 15 different answers and none make any sense to me can some one please inform me properly.
 

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It has been covered but, The primary difference between .223 Remington and 5.56 is that .223 is loaded to lower pressures and velocities compared to 5.56. .223 Remington ammunition can be safely fired in a 5.56 mm chambered gun, but the reverse can be an unsafe combination. The additional pressure created by 5.56 mm ammo will frequently cause over-pressure problems such as difficult extraction, flowing brass, or popped primers, but in extreme cases, could damage or destroy the rifle. Chambers cut to .223 Remington specifications have a shorter (throat) area as well as slightly shorter headspace dimensions compared to 5.56 mm "military" chamber specs, which contributes to the pressure issues.
 

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Siverado got it right. The problem is mostly in the chamber. Most guns would shrug off a 10% over pressure but that 10% can climb to catastrophic in the wrong chamber configuration.
 

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Michael,

They are not the same. The Throat on the 5.56 Chamber has a longer lead. While a "True 223 Remington Chambers lead is shorter. The Head Space on both are the same but the Chamber Lead is different in length. One should never shoot a 5.56 NATO round in a "True" 223 Remington Chamber" This is very obvious if you were to check the Chambers of both with a Throat Erosion Gauge. If you will go here in the Forum and find a Thread by me dated 8-23-11 Entitled Throat Erosion Gauge you will see pictures of the Throat Erosion Gauge and it's use. With the Throat Erosion Gauge inserted into the Receiver and looking straight down at a 90 degree angle as shown the "True" 223 Remington would only insert roughly before the First Line on the Throat Erosion Gauge from the tip of the gauge that is in the chamber and throat of the barrel. If it is a 5.56 NATO Chamber it will insert in until the the second or second and one half line prior to the third line. Some manufacturers have a slightly more open lead in their 5.56 chambers. Please see the Thread listed above! There is also one other issue. 5.56 Ammunition has higher pressure than commercial ammunition. Bottom line do not shoot 5.56 NATO Ammunition in a Remington 223 Chamber. All prominent name brand AR Rifles are 5.56 NAT0 or a Wylde Match Chamber which will shoot 5.56 equally as well.

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what they said^^

its kinda like a cars seatbelt, you wear it because something could happen. does it always happen no.. but it could. thats why we always advise to not shoot 5.56 out of a .223 chamber... but a 5.56 chamber can shoot both safely
 

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None..............
false.. even if you dont like the idea of non interchangability.

check all the measurments.. even though very little, there is a difference.
 

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Mods, since this comes up fairly regularly, perhaps this or one of the other resultant threads could be awarded "sticky" status?

http://en.wikipedia.org/wiki/5.56x45

5.56 mm NATO versus .223 Remington

The 5.56 mm NATO and .223 Remington cartridges and chamberings are similar but not identical. Military 5.56×45mm cases are often made thicker and therefore have less case capacity.[26] However, the NATO specification allows a higher chamber pressure. NATO EPVAT test barrels made for 5.56 mm NATO measure chamber pressure at the case mouth, as opposed to the location used by the United States civil standards organization SAAMI. The piezoelectric sensors or transducers NATO and SAAMI use to conduct the actual pressure measurements also differ. This difference in measurement method accounts for upwards of 20,000 psi (140 MPa) difference in pressure measurements. This means the NATO EPVAT maximum service pressure of 430 MPa (62,000 psi) for 5.56 mm NATO, is reduced by SAAMI to 55,000 psi (380 MPa) for .223 Remington.[27] 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)[28] 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.[29] 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.[30][31] 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.[32]
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 the 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 resultant litigation.
 

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Here is the best explanation from a guy who has shot and tested a crap ton of AR style weapons and REALLY knows his stuff. Well worth the read if you really want to be informed.
http://www.luckygunner.com/labs/5-56-vs-223/
 

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If you ever have any question get a Throat Erosion Gauge and measure the two of them. I have won a lot of free drinks over this in past years. Some of the newer military rifles have even a slightly longer lead over the standard 5.56 due to the fact the chamber is designed to shoot tracer rounds.
Most in the commercial market will never have exposure to this.
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And while we're on the subject of comparison the same cannot be said for .308 vrs 7.62 Nato which are identical pressures, although the NATO spec brass is a tiny bit thicker.
 

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7point62 said:
And while we're on the subject of comparison the same cannot be said for .308 vrs 7.62 Nato which are identical pressures, although the NATO spec brass is a tiny bit thicker.
Uh, no go. There's about 15,000 psi difference there. .308 shouldn't be used in a rifle chambered for 7.62 NATO.
 

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I use .308 Win. in my 2A exclusively & have for years, they just shoot better.............
 

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I'm not trying to discredit anything already said but, 5.56 can be shot from a saiga rifle chambered in 223. There is a stickie on the saiga 12 forum directly from the manufacturer. I personally have shot about 200 rounds of 5.56 out of my saiga 223 without an issue. I'm not saying that its true for all or any other rifle other than the saiga.
 

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Uh, no go. There's about 15,000 psi difference there. .308 shouldn't be used in a rifle chambered for 7.62 NATO.
Fortunately my Bushmaster MOE 308 is set up to fire both.

I did find the Luckygunner link 5.56 vs .223 – "What You Know May Be Wrong"
good info.
 
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