5.56mm vs. .223 cal.


-OR-


The Great Debate



CAUTION:

I have seen numerous forums and discussions regarding these two cartridges and the debate rages on apparently. First and foremost, there IS no debate here, the cartridges ARE different, this is a fact not a point of debate, end of story. However, if you want more reason, continue reading.

Very few expressing concern for the dangers...

The predominant attitude that I have seen and heard is all to cavalier for my thinking. I think it's a matter of human nature, in that, since gun incidents revolving around this "controversy" are rather rare, there is the powerful urge to minimize the actual dangers. That being said, the dangers are yet ever present. The 5.56mm cartridge is one of the most abundant and inexpensive on the planet, therefore, why would anyone want to gamble with the possibility of a catastrophic failure in their weapon by playing the odds and firing a cartridge they KNOW the weapons wasn't designed for.

It is one thing to gamble with your own well being, however, it's quite another to gamble with the well being of those around you. Where the manufacturers of barrels, gauges, reamers and cartridges strongly suggest against creating this risky situation. You wouldn't consider placing a 7.62mm cartridge in your .223 chamber. Why not? Simple.. Because it doesn't FIT! Shouldn't we be applying the same rationale here? We shouldn't place a 5.56mm cartridge in a .223 chamber. Doing so violates the first law of handling weapons, SAFETY! Gun accidents always happen when someone carelessly forgets simple gun safety and to knowingly endanger yourself and those around you, is simply ludicrous, irresponsible and criminal in the event someone gets injured.

Similar Cartridges

The .223 Remington and US 5.56mm ammunition are so similar that the cartridge cases would appear to be interchangeable. The specifications for the cases and the loaded ammunition are subtly, yet distinctly different, however. Although subtle, they may be enough to cause a severe problem, injury or death. This matter should never be taken frivolously nor should it be disregarded. If your weapon is chambered for 5.56mm, then you are likely good to go with either cartridge, however, if your weapon is chambered for .223, then you may indeed run risks if you fire the 5.56mm round, so don't do it.

If you EVER plan on shooting NATO 5.56mm ammunition in your AR, then DO NOT buy a .223 chambered barrel. Also consider, that the NATO 5.56mm cartridge is only the most common and widely available AR15 cartridge anywhere so why would you even consider purchasing a .223 chambered barrel. This is particularly true if the barrel is chromed as that reduces the clearances even more.

Here's the problem.

Many NATO cartridges have bullets that will become jammed into the rifling of a SAAMI chambering (the throat is too short). This is VERY DANGEROUS, for a great number of reasons.

SAAMI proscribes (denounces as dangerous or harmful) the use of 5.56mm military amm­u­nition in rifles chambered for .223 Remington. Remington was the orig­inal manufacturer of the ".222 Special" ammu­ni­tion designed by Eugene Stoner for the AR-15. This cartridge design was standardized as 5.56mm (5.56x45mm) by the US Army.

Concurrently, Remington added the cartridge to their product line as the ".223 Remington." How­ever, there are small, subtle differences between the two. If you hold the two cartridges side by side you won't be able to discern the differences, as they are several thousandths of an inch here and there. Army 5.56mm ammunition has more tolerance in the case neck diameter than the civilian SAAMI .223 Rem­ing­ton chamber drawing.

It is possible to fire .223 Remington cartridges in 5.56mm chambers. It is also possible to fire 5.56mm cartridges in .223 Remington chambers, BUT the tighter civilian chamber spec MAY cause certain types or lots of 5.56mm ammunition to fit too tightly for proper function and could cause severe damage or injury.

The .223 Remington is rated for a maximum of 50,000 CUP while the 5.56mm is rated for 60,000 CUP. That extra 10,000 CUP is likely sufficient to cause a failure in a chamber that's only rated for the "sporting" .223 Remington.

The .223 Remington and the 5.56mm NATO, when checked with a chamber GOOD reamer, also have discernable differences in the areas of freebore diameter, freebore length Leade and angle of the throat.

SAAMI
Technical Office:
P.O. Box 338
Branford CT 06405-0338

Here is the SAAMI position regarding this issue:

With the appearance of full metal jacket military 5.56mm ammunition on the commercial market, it has come to the attention of the Sporting Arms and Ammunition Manufacturers' Institute (SAAMI) that the use of military 5.56mm ammunition in sporting rifles chambered for Caliber .223 Remington cartridges can lead to higher than normal chamber pressures and possible hazards for the firearm, its user and bystanders.

Tests have confirmed that chamber pressures in a sporting rifle may be significantly higher in the same gun when using military 5.56mm ammunition rather than commercially loaded Caliber .223 Remington cartridges.

Military rifles have a different throat configuration than chambers for .223 Remington sporting firearms which, together with the full metal jacket of the military projectile, may account for the higher pressures which result when military ammunition is fired in a sporting chamber.

A firearm should be fired only with the cartridge for which it is specifically chambered by the manufacturer. 5.56mm ammuntion should not be fired in a weapon chambered for .223 Remington.

NATO chambers have a long Leade. SAAMI chambers are tighter and have a short leade. SAAMI chambers are designed for increased accuracy, but will yield dangerously high pressures in guns using military ammunition and/or which are subject to high volume shooting. Under such high pressures, a primer may back out completely, drop into the action and cause the firearm to stop working or worse.



A brief look at the headspace gauges should settle the question as to whether or not there are indeed differences between the .223 and 5.56mm cartridges. The reamers for the chamber as well as the headspace gauges ARE different. That fact alone should be enough to convince you of the differences. The chart below depicts the differences between the gauges for the two cartridges. Notice that each and every military gauge is longer than the .223 gauge. It doesn't take a rocket scientist or a gunsmith to recognize that the chamber lengths and configurations are different.


GaugeCivilianMilitaryMil Chamber Deeper by..
GO 1.4640 1.4646 +0.0006
NO-GO 1.4670 1.4706 +0.0036
FIELD 1.4700 1.4730 +0.0030


You might be saying, well, there's only a FEW thousandths of an inch difference here and there, that shouldn't be a big deal. Well my friend, trust me when I tell you there's only a few thousdandths of an inch difference between having a car engine run and having a car engine locked up. There's only a few thousandths of an inch difference between going to the moon or falling apart at launch. There's only a few thousandths of an inch difference between bolts and nuts working and every bolt on the planet falling out of the threads. There's only a few thousandths of an inch difference between a semiconductor and a pile of sand. Isn't it obvious that a mere few thousandths of an inch are anything but irrelevant and that the consequences of ignoring them can be catastrophic?



The good folks at AR15barrels.com have compiled the following charts to show us the differences between the chambers in the 223 and 5.56mm. These guys MAKE AR15 barrels, so if anyone should know, they should! We also thank them.
The following are courtesy of AR15barrels.com.

 223 and 5.56mm Reamer Dimensions
 223 vs. 5.56mm Reamer Comparison
 223 vs. 5.56mm Headspace Gauge Comparison


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Leade
Leade is the distance the projectile of a chambered round must travel upon ignition before it enters the bore of a barrel. It is measured in thousandths of an inch, and is a datum of considerable interest to benchrest shooters.