.223 Remington vs. 5.56 NATO: What You Don’t Know Could Hurt You

Bearing Arms ^ | 13 Feb, 2015 | Bob Owens

[MtnClimber]

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 5.56×45 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.

[Myrddin]

I wonder if there is also an issue between .308 and 7.62X51?

Significant differences. .308 Win has a tighter chamber than 7.62x51 NATO. The GO/NO-GO gauges are different for each chamber. I had a bad experience closing the bolt on a 7.62x51 NATO into a .308 Win chamber. Bang! Fortunately, the muzzle was pointed downrange and the bolt lugs locked sufficiently to restrain the brass. I've never used anything but .308 Win since and have had no problems. The box of 7.62x51 NATO remains in the safe and unused after 18 years.

[Myrddin]

My builds from parts always incorporate a Wylde chamber for .223. Anderson Rifles, Bearcreek Arsenal, and E Arthur Brown offer multiple lengths, twists, gas block diameters and finishes. My toolbox is full of AR-15 specific build tools. All well worth having to do a quality job. I'll never recoup the investment as "savings", but the build quality is hard to beat.

[Hugin]

Question

Ammunition, .223 & 5.56mm

Answer

All Bushmaster rifles are chambered to accept 5.56mm ammunition and always have been. The NATO Spec 5.56mm chambers have a longer “leade” or throat than the SAAMI Spec .223 caliber chambers which have about half of the leade or throat of the 5.56mm chambering. While it is safe to fire both 5.56mm and .223 caliber ammunition in our rifles, the 5.56mm ammunition should not be fired in rifles chambered in .223 caliber as they will develop very high pressures.

http://support.bushmaster.com/?title=General_Information/Ammunition,_.223_%26_5.56mm

[Myrddin]

Also a big issue with M1A rifles. They are timed for military ball ammo, you can blow one up with heavy (bullet weight) .308 rounds.

That's one of the reasons I still have only bolt action .308 rifles. My wife has a Ruger Deerfield .44Mag semi-auto. It is patterned after the Mini-14 with a rotary mag like the 10-22. The gas system is designed for 200 to 250 gr bullets. Any less and it won't cycle. Heavier will risk damage to the op-rod. She tried a "cowboy load" of 44mag designed for the single action shooters. It went bang fine. Couldn't find the brass. Cycled the bolt manually. Ping. Not enough gas. Replaced with PMC 240 gr JHP. Perfect cycling.

[wardaddy]

Are you a teen?

[jospehm20]

The article states that Armalite has fired millions of 5.56 rounds out of .223 rifles over 22 years with no catastrophic failures.

[JonPreston]

Thanks, I just looked at my Bushmaster and it does have the imprint; .223 and 5.56. This thread has been great as I had no idea about the difference in rounds.

[M Kehoe]

Thanks for the ping.

5.56mm

[Celtic Conservative]

The only prblems I’ve ever had between the two cartridges was about 12 years ago. I am a firearms instructor and armorer for a state law enforcement agency. During the Iraq war at times it was damned difficult to lay your hands on .223 for our Ruger mini 14’s for in-service requals. Back-ordered to the twelfth of never. Being desperate at one time we received an order of milspec 5.56 nato. After reviewing the armorers data on the mini 14’s barrels I accepted the shipment. Come qualification time the rounds chambered just fine. no failures to extract or eject. The problem was harder primers. Within a couple of hours all but 1 of 9 in service rifles had broken firing pins. I ended up sending back the balance of the shipment and told our supplier “.223 or nothing”. I then spent the next day OFF the range replacing firing pins. Grrr!

CC