5.56mm NATO versus 223 Remington Chamber Differences

[dukebri000]

very good and informative post. thank you

[swedeboy]

Great information, very helpful!

[Ned Christiansen]

I've posted this before but I think it bears retelling.

From a guy at ATK / Federal:

"As case in point, I fired XM193 5.56 ammunition in a 223 test barrel with average pressures (conformal transducer) of 72,550 psi, and peak pressure registered at 76,250 psi. Continued shooting of 5.56 ammunition in guns not chambered for 5.56 will show many warning signs of over-pressure, such as flattening of primers, smearing of the head stamp, dropped primers, blown primers and pre-mature wear on extractors and bolts.

It needs to be mentioned, however, that several civilian manufacturers of AR15 type rifles have not adhered very tightly to the necessary chamber/throat dimensions of 5.56, while marking their barrels as “5.56 NATO”.

It is my assumption that this is happening for two reasons: there is a belief that a rifle will shoot more accurately if the throat causes early engagement of the bullet to the rifling, although this is not necessarily proven.

The other reason is likely that manufacturers, under extreme duress to supply large numbers of rifles, are not replacing reaming tools early enough.

Because of this, some manufacturers’ rifles have a tendency to show signs of over pressure when shooting 5.56 ammunition, up to and including dropping and blown primers. This problem is easily remedied by judicious use of a finish reamer to provide that important amount of needed space, or to limit the rifle to a 223 diet."

[hunt_ak]

Thought this pics was good from Brownells courtesy of ar15barrels.com

[Edward78]

Very informative

[hafferf]

Hello Fellas;
I pretty much a Newb when it comes to an AR-15. I just bought one yesterday, a Bushmaster XM15-E2S M4. I just made inquirey in another thread about what I could shoot out of it. I gather from reading this thread that I can use 223 in this weapon, but not 5.56. I thought they were the same. Or am I still wrong...
Confused Senior Citizen.... (perhaps that is my problem)
Thanks again for any info
Fast Freddie

[Todd00000]

This article is from June 2012.

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

[hafferf]

Thank you Tod00000, for the information. My barrell is stamped "5.56" so I'll grab my pack and trudge on...;>)))
Thanks again for the info
Take care
Fred

[hotrodder636]

I find this thread very informative. Thanks to all of those who gave input for the rest of us.

[platoonDaddy]

Great thread.

Have this question, regarding my Colt SP-1 manufactured 1975.

The receiver is marked .223 and always assumed it was manufactured for Military specs. As of this date and time, there hasn't been any issue with 5.56 or .223.

Recently informed if the receiver is marked .223 and as long as the barrel is stamped C MP CHROME BORE it will safely handle 5.56. Inspected the barrel and there isn't any stamping.

What am I missing?