What is the difference between 223 & 556

[RDA]

Soooo just curious... why aren't there 556 reloading dies and load recommendations?

With respect to the dies, I always assumed it was because .223 can be used in both chambers whereas 5.56 can't so why make dies in the more restrictive chambering.

As already pointed out, there are 5.56 published loads.

[Steve RA]

Realistically, nothing to worry about.

[bfilbey]

The biggest difference is freebore. Freebore is the distance from the bullet to where it engages the lands in the rifling. .223 is a little tighter and CAN (not necessarily will) cause high pressure in a minimum spec chamber. Another difference with .223 bolt guns is twist. .223 bullets were typically light varmit bullets. The heavier 5.56 may not stabilize in a .223 bolt gun. My Remington bolt gun has a 1 in 12 twist, no good for the 69 gr and heavier bullets.

[RPatton]

Soooo just curious... why aren't there 556 reloading dies and load recommendations?

As for the dies it is because the chambers are the same with the exception of the neck length of the chamber.

Now that you mention it they could sell more dies that way.

And yes, some manuals do have 556 load data.

[bigedp51]

What is the difference between 223 & 556

The European CIP the equivalent of the American SAAMI considers the .223 and 5.56 to be one in the same cartridge. (the same for the .308 and 7.62)
And as soon as you can grasp thousandths of an inch and being American and millimeters being European and the metric system the answer will be NO difference. All Military chambers are larger in diameter and longer in headspace than their civilian counterparts. This compensates for the dirty conditions of combat and insures the firearms functions.

Early .223 rifles have a throat length of .0250, in 1979 the military increased the bullet weight of the M855 cartridge and increased the throat length to .0500 to compensate for this in the M16 rifle.

My Savage .223 with a 1 in 9 twist has a throat length of .0566 and this chamber is big enough for the M855 cartridge with room left over for the Savage company lawyer.

5.56 vs .223 – What You Know May Be Wrong

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

[FlashAndPoof]

I haven't really seen any difference between 223 and 556 ammo from just shooting it.

[bigedp51]

What is the difference between .223 & 5.56

The difference is in the United States we do not measure bullet diameter and case dimensions in millimeters.

In the United States our speed limits are in miles per hour and not kilometers per hour.

And our 30-06 was invented before NATO so we do not call the 30-06 the 7.62x63.

Bottom line, the European CIP is the equivalent of our American SAAMI and the European CIP considers the .223/5.56 and .308/7.62 the same cartridge. All military chambers are typically larger in diameter and have longer headspace limits and we still use the same reloading dies for both chambers.

The actual differences are are throat lengths, with some .223 rifles having a 1 in 14 or 1 in 12 twist rate for lighter bullets and a shorter throat. Now to add more confusion my Savage .223 with a 1 in 9 twist has a longer throat than my AR15 rifles.

Read the link below.

5.56 vs .223 – What You Know May Be Wrong

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

Below and remember "BOTH" the .223 and 5.56 are both rated at a maximum chamber pressure of 55,000 psi.

The first green bar on the left is factory loaded .223 ammunition fired in a .223 chamber and the pressure recorded was just below 50,000 psi. The second green bar from the left is a .223 fired in a AR15 with a longer throat with a chamber pressure of 45,000 psi.

The first blue bar on the left is a 5.56 fired in a short throated .223 rifle with a chamber pressure of just below 60,000 psi. And this caused a 5,000 psi increase in chamber pressure or 5,000 psi above its rated chamber pressure. The second blue bar on the far right is a 5.56 fired in a AR15 rifle and a chamber pressure of 55,000 psi.

NOTE: All these variations in pressure are due to the different throat lengths and my .223 has a even longer throat length. Many of the newer .223 rifles have a chamber big enough for any cartridge and room for the company lawyer to fit in also.