[MtnClimber]

I have heard of possible issues for years, but never an explanation.

[Ruy Dias de Bivar]

My newly purchased M-4 COLT has 5.56MM on the box, and the serial number. The same COLT rifle has .223 stamped on the rifle and the same serial number.

I have fired BOTH cartridges in a RUGER Mini-14 and other rifles with no problems.

[Reno89519]

I specifically bought a 5.56 to avoid the potential issues of buying .223 and using both ammo. So far I have strictly used 5.56 ammo in my Armalite Eagle-15.

[Fiddlstix]

Gimme a break. .223 is imperial measurement while 5.56 is metric measurement for the same cartridge.
Good grief

[Squantos]

Wylde about the potential ...... :o)

[Jumper]

That’s cool;) I only buy 5.56mm for target practice, but for personal defense I have 30-round mag’s (27 rounds) filled with .223 hollow points.

[mountainlion]

When reloading most sort out the military brass and the Commercial brass for the same capacity reason. Some go as far to weigh the brass for consistent loads.

[Drew68]

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.

The Armalite Eagle-15 I picked up last June is chambered in .223 Wylde. That's what sold me on it.

[Hugin]

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.

Does anyone know of any cases of catastrophic damage to the gun, let alone injury to the shooter? It may not be ideal, but I suspect the dangers are overblown. Reloading could be a problem I suppose. Personally I don't own any of either caliber, but I wouldn't hesitate to use 5.56 in a 223.

[Elderberry]

I have a similar issue with my Garands. .30 M2 vs 30-06 Springfield

[SkyDancer]

If the .30 carbine was good for great grandad in the Pacific it’s good enough for me. Love shooting the M1; been told it’s like a .357 magnum.

[JonPreston]

I have a Bushmaster AR-15, can I use 5.56?

[Buffalo Head]

This is one of the better layman articles published on the subject. There is little to criticize from a technical standpoint about what the author wrote.

He did, however, omit two important differences between the cartridges.

1. Pressures in commercial .223 Remington cartridges and 5.56mm NATO cartridges are determined by two entirely different systems and have different maximum pressure limits. The pressure limits are not interchangeable.

2. In the recent transitioning from the 5.56mm Ball M855A1 to the M855A2 cartridge, the pressure limit for the A2 cartridge was increased to achieve equivalent velocity to the older A1 round. The maximum pressure differential between the .223 Remington and 5.56mm cartridges are now even greater than when the non-interchangeability warnings were first issued. Yes, you might escape catastrophic gun damage and personal injury by ignoring warnings from entities who have far more knowledge about the subject than yourself. Same with firing +P cartridges in guns not designed for the higher pressures. But why would anyone voluntarily take such a foolish risk with no tangible reward other than saving a few pennies?

[fireman15]

There is almost an identical issue with .308 vs 7.62x51. Only in this case it is the civilian .308 which are typically loaded for higher pressures. Despite this the military brass is actually heavier. I use mostly surplus once fired 7.62x51 military brass to make up cartridges, but I also save the brass from civilian .308 that I have purchased over the years. In the rifles we use and with the recipes I carefully follow... it is not a safety issue, but the brass needs to be kept separated or you will definitely end up with cartridges that do not behave the same when they are loaded with the same powder charge and projectile. And I have confirmed this with a chronograph.

[JoeProBono]

5.56x45 NATO vs .223 Rem How To Determine Your Rifle Chamber

https://www.youtube.com/watch?v=xepLT-x58JQ

[Carriage Hill]

Here’s a better and more technical explanation of 5.56 v .223 ammo:

http://www.luckygunner.com/labs/5-56-vs-223/

[TonyM]

If the barrel is not stamped 5.56 then don’t put a 5.56 cartridge in it. It really is that simple. A 5.56 barrel can handle the pressure from a .223 but a .223 barrel cannot handle the pressure from a 5.56.

[jonno]

bookmark

[ChildOfThe60s]

RRA LAR 15 with a Wylde Chamber. I’ve shot thousands of rounds of .223 & 5.56 Nato through it.

[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