Often asked ---5.56 vs 223 question

[sirdanny4011]

Yes I did a search but could not find what I was looking for. So please bear with me.

 

I am in the process of buying my first AR. When reloading does it matter if I use 223 or 5.56? And I use a 223 Head Stamp shell with a 5.56 load and vice versa? 

 

Thanks and sorry about my lack of knowledge on this.

 

Edit: Oh! And does the reloading dies make a difference? Some say 223/5.56 and some just say 223.

Edited February 16, 2014 by sirdanny4011

[tnhawk]

My reloading manuals don't show a difference.

[Guest theconstitutionrocks]

ok...I can't speak to the reloading aspect but what I CAN tell you is that .223 and 5.56 are NOT the same round. Bear with me, but if memory serves me correctly, while the bore diameter is the same, it is the neck (leade) as well as the rifle chamber that is the issue. The 5.56 has a SLIGHTLY longer neck. As such, when a 5.56 round is chambered in a .223 weapon, the projectile is already slightly in contact with the rifling of the bore prior to firing (this is not supposed to happen). As a result, at the moment of firing, this creates a pressure spike beyong the rated capacity of the weapon which can cause a catastrophic failure of the weapon (it blows apart).

 

I have heard people say that you can overcome this by seaating the projectile slightly further into the casing during reloading. I don't know enough about reloading to make an informed comment on that. What I will say is that (my understanding) you can use .223 in a 5.56 weapon but not the other way around. 

[Guest Brutnus]

556 is like 49/1000s longer, more pressure and has a faster FPS. 

[z0mbies fear me]

Dimensionally loaded 223 and 5.56 is identical. The difference is pressures. SAAMI spec for 223 is 55K psi and 5.56 is more than that. Most estimates is 5.56 runs 65K.

Now because of the additional pressures of 5.56 the chamber is slightly different than a 223 chamber. The chief difference is the throat in a 5.56 is slightly longer than 223. This allows the bullet to begin moving, and reduce pressures, before hitting the resistance of the rifling.

Because of the longer throat of the 5.56 chamber it is safe to shoot 223 in a 5.56 chamber.

Some say that you cannot shoot 5.56 in a 223 chamber. But I have shot a lot of 5.56 out of guns with a verified 223 chamber. Shooting 5.56 in a 223 will not cause some sort of dramatic failure. If it does then your gun had issues in the first place. Proof loads are well beyond the pressures encountered when shooting max 5.56 loads in a 223 chamber.

Then there is the estimate that 25% of the "5.56" actually have 223 chambers. As manufacturers chamber barrels the reamers dull and most resharpen the reamer. This reduces the size of the reamer each time. There was a random test done by a publication and well over 25% had 223 chambers so if shooting 5.56 in a 223 chamber caused the gun to blow up we would be seeing it everyday.

[z0mbies fear me]

From... http://www.tngunowners.com/forums/topic/75797-difference-between-223-and-556/?view=getnewpost Edited February 16, 2014 by z0mbies fear me

[gregintenn]

Same brass. Same projectile. Same reloading dies. Slightly different chamber dimensions.

 

I've fired both interchangeably with no ill effects. Your mileage may vary.

 

I don't think I've ever seen any commercially produced reloading data for 556.

Edited February 16, 2014 by gregintenn

[TNMTBik3r]

A couple of my manuals specifically have a section on 5.56. But it is only one or 2 pages and limited info.
Just use .223 reloading info and your good to go. No need for the higher pressures just for shooting.

[Luke E.]

 As far as reloading goes you'll be just fine. When it comes to loading your own it doesn't matter if 5.56 factory ammo is longer. If you follow the published reloading data they will end up the same length no matter what the head stamp is, after all an inch is an inch is an inch correct? Yes. I have loaded and run a great many 5.56 cases through a .223 chamber with no measurable difference. When buying factory ammo I would stay away from running 5.56 in a .223 only chamber because the .223 chamber is not rated for as much pressure as the 5.56 chamber is. There are no "5.56" specific reloading dies that I know of as they are one and the same. You may already know this but 5.56 (and some .223) brass has a crimped primer pocket and this crimp will have to be removed before pressing in a new primer.

[DMark]

Just remember this simple numbers trick.....

 

Smaller can go into Bigger.

 

223 into 556.

 

But Bigger can't go into Smaller.

 

556 into 223.

 

AND - - - What is important is the markings on the barrel in regard to caliber, not what the lower's rollmark might say.

[Rowdy]

Just remember this simple numbers trick.....
 
Smaller can go into Bigger.
 
223 into 556.
 
But Bigger can't go into Smaller.
 
556 into 223.
 
AND - - - What is important is the markings on the barrel in regard to caliber, not what the lower's rollmark might say.

And to muddy the water further, the opposite is true of .308 and 7.62X51...