What determines 223 vs 556

[1 SIG fan]

my lower is stamped 223. I understand mags are the same. Would i just need a new barrel if I wanted to shoot 5.56?

I want 5.56 so I have the ability to shoot both cal's, but how. Thanks.

[SJgunguy24]

Make sure your rifle has a 556 chamber. The 556 is loaded to a higher pressure and there are slight differences in the case geometry.
With the 556 chamber you can shoot 556 and 223
I'm sure Randall will be here soon, he's the AR guru.

[NiteQwill]

The barrel must be marked/made to shoot 5.56.

You cannot (should not) shoot 5.56 out of a .223 barrel.

Your lower has nothing to do with it.

[Flogger23m]

I would like to know how your upper is marked in 5.56.

I have a CMMG 16" midlength. 1/7 twist. Not sure if it is 5.56 or .223 though.

I don't see any markings on the barrel. Are the markings covered up by the handguards?

If so, how do I remove them so I can check?

[djleisure]

I would like to know how your upper is marked in 5.56.

I have a CMMG 16" midlength. 1/7 twist. Not sure if it is 5.56 or .223 though.

I don't see any markings on the barrel. Are the markings covered up by the handguards?

If so, how do I remove them so I can check?

The upper will not be marked - the barrel will be. Usually somewhere towards the end of the barrel or middle of the barrel. CMMG is good to go with 5.56 - now worries there.

[WebMoskal]

What determines 223 vs 556

Also, 10,000 posts determine the difference

[akjunkie]

This is a must read for all AR enthusiast.

Get Educated..

http://ammo.ar15.com/ammo/

[1 SIG fan]

I TOTALLY understand the size and pressure difference between the two rounds.

The question is: What ON THE RIFLE determines which cal is to be used. my .223 stamped lower isn't capable of shooting 5.56. WHY?

So, i can use same lower, mags, bolt carrier group etc... Just need new barrel 5.56?

[1988]

The barrel must be marked/made to shoot 5.56.

You cannot (should not) shoot 5.56 out of a .223 barrel.

Your lower has nothing to do with it.

That's the good rule.

However, Saiga 223 is known to handle 5.56 very well.

[sevensix2x51]

I TOTALLY understand the size and pressure difference between the two rounds.

The question is: What ON THE RIFLE determines which cal is to be used. my .223 stamped lower isn't capable of shooting 5.56. WHY?

So, i can use same lower, mags, bolt carrier group etc... Just need new barrel 5.56?

the lower markings have nothing to do with it. if the barrel of the rifle is marked 5.56 nato, you can shoot it. the only danger between them is the pressure in the chamber, so as long as your barrel is rated for 556, you will be fine.

you can shoot .50bmg on a 223 lower if you have the right upper assembly.

[SJgunguy24]

That's the good rule.

However, Saiga 223 is known to handle 5.56 very well.

The Saiga 223 is rated for 556

[1 SIG fan]

the lower markings have nothing to do with it. if the barrel of the rifle is marked 5.56 nato, you can shoot it. the only danger between them is the pressure in the chamber, so as long as your barrel is rated for 556, you will be fine.

you can shoot .50bmg on a 223 lower if you have the right upper assembly.

Perfect! Thank you for the concise answer!

[bomb_on_bus]

All other components of the rifle can be used either on 5.56mm or .223cal except the barrel. The parts are universaly the same for either round. Theres no difference in magazine size, BCG dimensions, lower mil specs, trigger groups, etc. What ever you could put on an AR15 will work for either round. Again the barrel is the only difference between the 5.56 and the .223 platform.

A .223 cartirdge will work in either a 5.56mm or a .223cal barrel, but a 5.56mm won't work in a .223cal barrel due to the much higher PSI created from the 5.56 round vs.the .223cal round.

I hope that helps

[Army]

It's not higher loaded pressure, it's the throat leade length. Military cases are "harder" than commercial, and have relatively thick necks. Thus they do not expand as quickly as commercial during firing. The short leade of the .223 chamber physically blocks the bullet before enough pressure builds to get it into the rifling.

.223 cases easily expand, and the bullet has a short free run before engaging the rifling.

Wylde chambers compromise between the long leade of the .223, and the short leade of the 5.56, allowing both bullets to have a short free run before engaging the rifling.

[tkrrox]

how about in a bolt action? can you shoot 5.56 out of a remington 700?