# .223 vs 5.56 ammo



## Iron Bear (Nov 19, 2008)

Are they interchangeable. I got an AR for Christmas and it is stamped 5.56 so I’m wondering if I can us some bulk .223 ammo I have.


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## Lone_Hunter (Oct 25, 2017)

size wise, they are identical, however, 5.56 has higher chamber pressure then a 223.

What this means is that:
- if a rifle is chambered for 556, you can shoot 556, and 223. 
- If a rifle is chambered for 223, you should only be shooting 223, and shouldn't be using 556.


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## Bax* (Dec 14, 2008)

Lone_Hunter said:


> size wise, they are identical, however, 5.56 has higher chamber pressure then a 223.
> 
> What this means is that:
> - if a rifle is chambered for 556, you can shoot 556, and 223.
> - If a rifle is chambered for 223, you should only be shooting 223, and shouldn't be using 556.


Good simple explanation. Iron, your AR likely has a Wylde chamber as most do. But a few ARs are chambered exclusively for 223 (I had one). So some guys need to be careful with which ammo they feed it.


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## Iron Bear (Nov 19, 2008)

Thanks for clarifying guys


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## DallanC (Jan 13, 2009)

Lone_Hunter said:


> size wise, they are identical, however, 5.56 has higher chamber pressure then a 223.


NOT true. 223 has a throat of .253" where 5.56 is .251", its close but enough of a difference to matter.











> What this means is that:
> - if a rifle is chambered for 556, you can shoot 556, and 223.
> - If a rifle is chambered for 223, you should only be shooting 223, and shouldn't be using 556.


True.

-DallanC


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## Lone_Hunter (Oct 25, 2017)

Well, geez, if you want to get technical about it. I'm not even sure that .002 in the throat makes a difference even if you were reloading those cartridges.


As an aside to Iron bear, check your twist rate. It's probably 1/9. Most AR's these days are 16" barrels in a 1/9 twist. Unless you got something real fancy for Christmas.


From my experience, the difference in twist rates doesn't make much of a difference inside 100 yards. Try for a 200 yard zero however, and the difference in projectile weights and twist rates is far more pronounced. I wish my AR didn't have a 1/7 twist, but that is my fault. :roll: For my rifle, (20" 1/7) at 200 yards, 55 grain is minute of man, 75 grain is minute of angle. 



Your mileage will vary.


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## DallanC (Jan 13, 2009)

Well it all is cumulative. 

5.56 also have thicker case walls, which means less internal case capacity which in turn means higher pressures. 

I love the heavier LC brass for all of my reloading except for one single load. I stumbled on a load using PMC brass and 65gr Sierra BT's... they go .38-.39" out of my Stag 6L AR15. Amazing rounds from a semi-auto.

-DallanC


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## Lone_Hunter (Oct 25, 2017)

Well, you are right. Reloading is an exact thing. I haven't bothered with reloading in awhile, but I was pretty anal about it while I was. All it took was 1 squib, and I was sorting, measuring, weighing, and case gauging ....EVERYTHING.


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