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5.56 vs. .223


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This is probably a stupid question, but here goes:

 

What is the difference between 5.56mm ammunition and .223 Remington ammunition?

 

I have always believed there is no difference, and have fired surplus 5.56 and civilian .223 through my ARs with no problems for several years now.

 

I recently read an article (I wish I could remember where!) that made a statement to the effect of "5.56 and .223 are similar but not identical."

 

What's the truth here? Am I harming my rifles by using the wrong ammo?

 

Thanks for any help.

Collecting 3rd Armored Division items of all kinds from all eras, specializing in the 36th Armored Infantry Regiment.

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They are technically 2 different cartridges made on tooling cut to slightly different measurement specifications, one in inch measurements and the other in metric. .223 inches actually converts to 5.66mm. Most AR platform rifles will chamber and fire either round with no problem. I have never heard of any issues and I believe it is safe to interchange in the civilian AR rifles. Some civilan hunting rifles may have their chamber cut for the slightly larger .223 cartridge.

 

Essentially the cartridges are identical in size, with the exception that .223 ammunition made on true inch-system tooling is slightly larger than standard 5.56mm ammunition. Ammuntion made for military contracts is made to the 5.56mm spec and m4/m16 series rifles have their chambers cut to this spec. Usually the guns are stamped under the barrel as to their caliber and generally it says "5.56"

 

I imagine there might be some difficulty in chambering true .223 ammuntion in a gun with a chamber only cut for 5.56mm ammuntion. The fit would be very tight to say the least.

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This is probably a stupid question, but here goes:

 

What is the difference between 5.56mm ammunition and .223 Remington ammunition?

 

Ya know...I've had that same question for years. I was never bold enough to ask anyone. I've fired ARs and held (not fired) many M-16s. The rounds looked identical to my untrained eye.

 

When I heard 5.56 I always thought that it was merely a more NATO-friendly designation for .223. To know that there is actually a difference between the rounds is interesting.

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.223 will work in 5.56, but 5.56 will not work in a .223-only marked rifle. In my reading, the difference is when the riflings begin compared to the shape of the bullet. I am told a 5.56 will contact the rifling on a .223 when the bolt is closed, causing a bit of a problem with pressure and etc.

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WWII US Navy Uniforms from the Battle Off Samar: USS Johnston DD-557, USS Hoel DD-553, USS Samuel B. Roberts DE-413, USS Heermann DD-532, USS Dennis DE-405, USS John C. Butler DE-339, USS Raymond DE-341, USS Fanshaw Bay St. Lo, White Plains, Kalinin Bay, Kitkun Bay and Gambier Bay...


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.223 will work in 5.56, but 5.56 will not work in a .223-only marked rifle. In my reading, the difference is when the riflings begin compared to the shape of the bullet. I am told a 5.56 will contact the rifling on a .223 when the bolt is closed, causing a bit of a problem with pressure and etc.

Correct, I've got an Bushmaster AR-15 which chambers both .223 and 5.56 without any issues in performance(accuracy) or function. It even states in the AR-15 manual that the rounds are interchangeable for this weapon. However, because the 5.56 will produce more pressure(hotter and faster), it will then affect function in a .223 specific rifle which will in turn have the obvious affect on performance. Most manuals which come with civilian .223 specific rifles will even state to use .223 ONLY in the weapon.

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A friend who is a reloader once told me that NATO-spec 5.56 is "not fussy" and will shoot WELL in any military-style AR rifle or an FNC or AUG etc. This came up when he was running off a batch of 5.56. HOWEVER, civilian .223 IS "fussy" and varies from one manufacturer/nationality to another. Mostly it has to do with the BULLET (bullet weight is part of it in a minor way, and powder choice CAN affect the outcome) and, within that realm, with the bullet seating in the chamber/feeding.

 

This is aggravated in using softpoint hunting ammo in military style weapons. He was among other things a police armorer/rangemaster and he diagnosed problems his dept was having with Ruger Mini-14s/AC556s AND with Colt made AR-15s as coming from using TOO GOOD civilian ammo. IIRC he said Norma was the "worst" in this because it was such high-quality (brass at least). He advisaed the dept to get ammo from DOD or buy milspec S Korean and/or Filipino fodder. Civilian stuff is generally optimized for bolt-action rifles, and does not worry about cycling in semi-autos and surely not in full-auto or belt-fed use.

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.223 will work in 5.56, but 5.56 will not work in a .223-only marked rifle.

 

I disagree. I have a Remington 700 chambered in .223 and have fired 5.56 through it. The difference is the case thickness. Externally, they are the same size, however, 5.56 has thicker brass to handle the excessive chambers for automatic weapons. Machine guns tend to have very sloppy chambers so that they don't jam as readily when trash gets introduced in the chamber with the round. Therefore, the brass must be thicker to handle the amount of expansion during the firing process. .223 ammo fired in a machine gun would have a much higer incidence of split brass than 5.56 ammo. Because of this, the 5.56 has a smaller internal dimension and thus can create higher pressures than the 5.56. If you fire 5.56 in a .223, you need to watch for flowing brass, popped or greatly deformed primers. These are all signs of excessive pressure and you should stop. There are some issues with the leade and if the bullet is touching the lands on loading, that can also create higher pressures than if the bullet has to jump to the lands.

I have been reloading for almost 20 years and I prefer 5.56 brass for my .223 because it has more life cycles than .223 brass, you just have to load it with a little less powder than you would for a 5.56 weapon. These rounds used in my .223 are worked up until I begin to get signs of excessive pressure and then backed off. In my rifle, the difference is .2 grains. The excessive pressure most likely will not make your gun blow up, but will cause rapid wear on your bore and significantly reduce the life of your barrel.


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I disagree...

You're probably be right and I'd be willing to do the same thing concerning my own weapons but, I think that in the case of a civilian sport rifle in .223 it is better for us to stick with manufactures recommendations when giving advice here on the forum

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"Cheaper then dirt" has this article on their website.

 

Is 5.56mm safe in my .223 Remington?

 

The .223 Remington is a sporting cartridge with the same external dimensions as the 5.56x45mm NATO military cartridge. It is loaded with a .224" diameter, jacketed bullet, with weights ranging from 40 up to 90 grains, though the most common load by far is 55 grains.

 

The primary differences between .223 Remington and 5.56 x 45 mm (NATO) are that .223 Remington is loaded to lower pressures and velocities compared to 5.56 NATO and the 5.56 NATO chamber has a longer leade. .223 Remington ammunition can be safely fired in a 5.56 NATO chambered gun, but the reverse can be an unsafe combination. The additional pressure created by 5.56 NATO ammo will frequently cause over-pressure problems such as flowing brass, difficult extraction, or popped/punctured primers, but in extreme cases, could damage or destroy the firearm. Chambers cut to .223 Remington specifications have a shorter leade (throat) area as well as slightly shorter headspace dimensions compared to 5.56 NATO "military" chamber specs, which contributes to the pressure issues.

 

While the 5.56 NATO and .223 Remington cartridges are very similar, they are not identical. Military cases are made with thicker brass in the web area than commercial cases, which reduces the powder capacity (an important consideration for handloaders), and the NATO specification allows a higher chamber pressure. Test barrels made for 5.56 NATO cartridge measure chamber pressure at the case mouth, as opposed to the SAAMI (Sporting Arms and Ammunition Manufacturer’s Institute) location. This difference accounts for upwards of 20,000+ psi difference in pressure measurements. That means that advertised pressure of 58,000 psi for 5.56 NATO, is around 78,000 psi tested in .223 Remington test barrels. SAAMI .223 Rem Proof MAP is 78,500 psi so every 5.56 NATO round fired is basically a proof load, potentially very dangerous. The 5.56 NATO chambers, also known as mil-spec chambers, have a longer leade, which is the distance between the mouth of the cartridge and the point at which the bullet engages the rifling of the barrel. The .223 Remington chambering, known as the "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, used by Rock River Arms or the Armalite chamber, which are designed to handle both 5.56 NATO and .223 Remington equally well.

 

Using commercial .223 Remington cartridges in a 5.56 NATO chambered rifle should work reliably, but generally will not be as accurate as when fired from a .223 Remington chambered firearm due to the excessive leade. Using 5.56 NATO mil-spec cartridges (such as the M855) in a .223 Remington chambered firearm can lead to excessive wear and stress and even be unsafe, and the SAAMI recommends against the practice. Some commercial fireams marked as ".223 Remington" are in fact suited for 5.56 NATO, such as many commercial AR-15 variants and the Ruger Mini-14, but the manufacturer should always be consulted to verify that this is acceptable before attempting it. Signs of excessive pressure (such as flattening or puncturing of the primers) should also be looked for in the initial testing with 5.56 NATO ammunition.

HHC 3/39th Inf. Bn., 9th ID 76-79
IAFF L-726 - retired.

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Thanks guys!

 

I'm glad I asked.

 

I checked my rifles, and my older Colt SP1 (M16A1 look-alike) is marked .223 Remington while my Smith & Wesson M&P-15 (M-4 wannabe) isn't marked at all, despite what the owner's manual claims. The case that came with the gun is marked 5.56mm however.

 

I plan to contact both Colt and S&W for their take on it, but until then, will shoot .223 in the SP1 and 5.56 or .223 in the M&P.

 

Now - how about .308 vs. 7.62? Same situation?

 

Probably should start a new topic.

 

Thanks again for the great information!

 

Steve

Collecting 3rd Armored Division items of all kinds from all eras, specializing in the 36th Armored Infantry Regiment.

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Thanks guys!

 

I'm glad I asked.

 

I checked my rifles, and my older Colt SP1 (M16A1 look-alike) is marked .223 Remington while my Smith & Wesson M&P-15 (M-4 wannabe) isn't marked at all, despite what the owner's manual claims. The case that came with the gun is marked 5.56mm however.

 

I plan to contact both Colt and S&W for their take on it, but until then, will shoot .223 in the SP1 and 5.56 or .223 in the M&P.

 

Now - how about .308 vs. 7.62? Same situation?

 

Probably should start a new topic.

 

Thanks again for the great information!

 

Steve

 

SP1s, even though their reciever is marked 223, all their barrels/barrel extensions (chambers) are 5.56. You are good to go with 5.56, althought you may want to stick with 55gr projectiles due to the slower twist rate.

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