ar15 223/556

[jules]

If an lower is marked 5.56mm will it accept 223 and 5.56 ammo. and will all 223 uppers accept 223/5.56 also.

 

[CRSIII]

This might help.

http://findarticles.com/p/articles/mi_m0BQY/is_9_51/ai_n14816186/

 

[Underwhere]

If an lower is marked 5.56mm will it accept 223 and 5.56 ammo. and will all 223 uppers accept 223/5.56 also.

The upper is what you need to worry about.
If it says 5.56 it will shoot 223.
If it says 223 it will not shoot 556.

They are not backwards compatible.

So I would always suggest buying 5.56

 

[andy t]

The upper is what you need to worry about.
If it says 5.56 it will shoot 223.
If it says 223 it will not shoot 556.

They are not backwards compatible.

So I would always suggest buying 5.56

Just because an upper is marked 5.56 does NOT mean it is actually 5.56 - some manufacturers are known to cut corners/mismark uppers. Caveat emptor!
.223 will probably shoot 5.56, but there may be issues with functioning, etc...

 

[Skald]

Just because an upper is marked 5.56 does NOT mean it is actually 5.56 - some manufacturers are known to cut corners/mismark uppers. Caveat emptor!
.223 will probably shoot 5.56, but there may be issues with functioning, etc...

And if they do they do open themselves up to product liability (5.56N is loaded to a higher pressure than regular .223).

Now if it is .223 Wylde, then from what I gathered it will handle the higher pressure of the 5.56N load no problem.

 

[RKG]

The upper is what you need to worry about.
If it says 5.56 it will shoot 223.
If it says 223 it will not shoot 556.

They are not backwards compatible.

So I would always suggest buying 5.56

Actually, I'd go by the markings on the barrel (may have to remove the handguards to see them), not those on the upper.

 

[vellnueve]

The BARREL, as RKG notes, is the determining factor, not the receiver.