Fulton armory on their website discuss how their rifles are esentially an average of the throat difference between the .223 Remington and the 5.56X45 round.

www.fulton-armory.com/556-vs-223-Chambers.htm

I understand that a rifle listed as 5.56 will shoot .223 rounds but not the other way around.  The idea sounds promising as to keep some of the accuracy of the .223 round while not having to worry about a 5.56 round not chambering correctly.  Are there any other manufacturers out there that do this?  I understand the benifit, what would the downside to this be?

Retar Ted

www.ammo-oracle.com

Go here and read up, (see the second question IIRC) this is not a Fulton rifle issue (as all makers produce their rifles in varying chambers, depending on who it is), it's a chambering issue.

Best get up to speed by reading about it, there's also a "Brand Comparision" chart by Troy, tacked to the top of the AR Discussion Forum, IIRC, ya might want to check that out too......

Welcome

Mike

I understand that a rifle listed as 5.56 will shoot .223 rounds but not the other way around. The idea sounds promising as to keep some of the accuracy of the .223 round while not having to worry about a 5.56 round not chambering correctly. Are there any other manufacturers out there that do this? I understand the benifit, what would the downside to this be?

Not true at all.  You can chamber and fire 5.56 in a .223 chamber.

5.56 NATO is loaded hotter than the SAAMI spec for .223. The SAAMI spec was set long ago for the weakest civilian rifle on the market, thus their warning on not firing 5.56 in a .223.  However, the AR-15 and M16 are much stronger rifles.

Check the library, tech notes, at www.armalite.com.  And there are other mfgs who say the same.

I have fired a lot of 5.56 through one of my rifles that has a ".223 match" chamber with NO problems.  

If you hand load, will the brass have a shorter life span in a NATO chamber?

The chamber of semiauto, whether .223 or 5.56, is looser than bolt actions.  This is to allow easy cycling.  

The chamber, or that section from the neck on back to the case head, is the same in AR-15 type rifles whether .223 or 5.56.  It is only the throat that is different.

With semiautos it is recommended that you always full length resize.  Yes, you have shorter case life than in a bolt action that is neck sized only.

The difference in the .223 and 5.56 is the slightly longer leade or throat (the unrifled bore section just past the case neck).  That is the difference in the .223 and 5.56 chamber.

RetarTed, Armalite also uses in intermediate throat or leade on their .223.