yeah, could mean trouble...
Posted on 02/21/2011 7:37:41 PM PST by neverdem
Is firing a 5.56 NATO cartridge in your .223 Remington chambered AR15 dangerous? Or do Internet forum-ninjas and ammunition companies selling you commercial ammo instead of surplus overstate the dangers? Believe it or not, a real danger exists, and some gun owners who think they are doing the right thing may not be safe.
The Cartridges
The .223 Remington and 5.56x45 NATO cartridges are very similar, and externally appear the same. But there are some differences that lie beneath the surface.
The 5.56 case has thicker walls to handle higher pressures, meaning the interior volume of the case is smaller than that of a .223. This will alter the loading data used when reloading 5.56 brass to .223 specs.
Some 5.56 loads have a slightly longer overall length than commercial .223 loads.
The Chambers
The significant difference between the .223 Rem and 5.56 NATO lies in the rifles, rather than the cartridges themselves. Both the .223 and 5.56 rounds will chamber in rifles designed for either cartridge, but the critical component, leade, will be different in each rifle.
The leade is the area of the barrel in front of the chamber prior to where the rifling begins. This is where the loaded bullet is located when a cartridge is chambered. The leade is frequently called the “throat.”
On a .223 Remington spec rifle, the leade will be 0.085”. This is the standard described by the Sporting Arms and Ammunition Manufacturers’ Institute, Inc. (SAAMI). The leade in a 5.56 NATO spec rifle is 0.162”, or almost double the leade of the .223 rifle.
A shorter leade in a SAAMI spec rifle creates a situation where the bullet in a 5.56 NATO round, when chambered, can contact the rifling prior to being fired. By having contact with the rifling prematurely (at the moment of firing), chamber pressure can be dramatically increased, creating the danger of a ruptured case or other cartridge/gun failure.
The reverse situation, a .223 Rem round in a 5.56 NATO gun, isn’t dangerous. The leade is longer, so a slight loss in velocity and accuracy may be experienced, but there is not a danger of increased pressures and subsequent catastrophic failure.
How serious is the danger of firing 5.56 ammo in .223 guns? Dangerous enough that the SAAMI lists 5.56 military ammo as being not for use in .223 firearms in the technical data sheet titled “Unsafe Firearm-Ammunition Combinations.”
ATK, the parent company of ammunition manufacturers Federal Cartridge Company and Speer, published a bulletin entitled “The Difference Between 223 Rem and 5.56 Military Cartridges.” In this bulletin, ATK stated using 5.56 ammo in a .223 rifle could result in “…primer pocket gas leaks, blown cartridge case heads, and gun functioning issues.”
However, the danger may be lower than SAAMI or ATK suggest. In Technical Note #74 from ArmaLite, the company states “millions of rounds of NATO ammunition have been fired safely in Eagle Arms and ArmaLite’s® SAAMI chambers over the past 22 years,” and they have not had any catastrophic failures.
According to ArmaLite:
“Occasionally a non-standard round (of generally imported) ammunition will fit too tightly in the leade, and resistance to early bullet movement can cause elevated chamber pressures. These pressures are revealed by overly flattened primers or by powder stains around the primer that reveal leaking gasses.”
What Do You Have?
So, if you own a rifle chambered for the .223 for 5.56, do you know for which caliber it is really chambered?
Many match rifles are chambered in .223 Remington (SAAMI specs) for tighter tolerances, and theoretically better accuracy.
Many of the AR-15’s currently sold on the market are made for the 5.56 NATO cartridge. If you own one of these, you should be fine with any .223 or 5.56 ammunition.
However, ATK dropped this bomb in the bulletin on the .223/5.56:
“It is our understanding that commercially available AR15’s and M16’s – although some are stamped 5.56 Rem on the receiver – are manufactured with .223 chambers.”
So, even if your AR is stamped 5.56, is it really? Check your owner’s manual or call the company directly and make sure you get an answer you feel comfortable with.
As if the confusion regarding the .223 vs 5.56 chambers wasn’t enough, there is a third possibility in the mix, that is being used by at least one major manufacturer. The .223 Wylde chamber is a modified SAAMI-spec .223 chamber that allows for the safe use of 5.56 NATO rounds, but maintains tighter tolerances for better accuracy.
Yeah, yeah… What’s the bottom line?
Here’s the bottom line. If you want to follow the safest possible course, always shoot .223 Remington ammunition. The .223 Rem cartridge will safely shoot in any rifle chambered for the .223 or 5.56.
If you want to shoot 5.56 NATO rounds, make sure you have a rifle designed for the 5.56 military cartridge. Shooting 5.56 in a normal .223 Rem rifle can result in bad things.
Believe it or not, a reverse condition exists with the beloved .308.
By reverse, I mean an increased failure risk in some rifles to use civilian .308 in a NATO spec 7.62X51mm chamber. Some of the hundred plus year old pre 1898 mausers converted to 7.62X51mm come to mind.
A. Yes you can, the Mini 14 has always had a 5.56x45 chamber.
The mini14 receiver is marked ".223 CAL" not ".223 rem."
If you reload your own ammo and are careful to keep the charges out of the max muzzle velocity range and keep the overall length of the finished cartridge at the .223 Remington spec., using once fired 5.56 brass should not pose a problem.
What the article tells us is that using FACTORY loaded NATO 5.56 in a weapon — like the Mini-14 — chambered for .223 can cause a problem.
sfl
OT
Met an Army Sniper in between tours who sold me a Glock working at the local gun shop this weekend. He said they use .308 bolt and M-16 exclusively unless they need to shoot through a car or cinder block then they use 50mm. I asked why they don’t use a .300 win mag and he said the Army is converting over to them soon. FWIW
You're correct. The manual that came with my mini-14 clearly spelled that out.
yeah, could mean trouble...
To the novice, the two rounds look identical.
Me too.
50 MM, Holy super bore Batman,That'll knock your fillings loose. ;-)
LOL, when you start worrying about the thickness of the copper/brass you have a problem but it has nothing to do with the firearm. LOL
damn, i'd thought they'd go for the .338
I would not worry much about the Mauser 98’s. Now the Spanish Mauser 95’s are another issue. Some were converted to a homegrown round dimensionally identical to the 7.62x51. With only two locking lugs and the inferior Spanish steel, there is a very serious problem.
Surprising, not really, they use the 50 very seldomly, so he said, because it weighs 28 pounds.
BFLR
The Bradley Fighting vehicle has a 25 mm gun.
I was just poking fun at your typo.
When he said .300 win mag, I thought he’d say the Weatherby .300 mag which IIRC has a higher velocity and less drop according to my recipe book.
Not familiar with the .338 though...
LOL!
Yeah, metric vs imperial conversions weren’t taught very well at my Publik Skrool...
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