.223 O.K. in 5.56 But Not Vice Versa?

[Abraham]

I hope the subject line isn't confusing, but to make my question more understandable: If a rifle is chambered for 5.56 is it also safe to shoot .223?

If a different rifle states .223 without mentioning 5.56 - should .223 only be used as 5.56 pressures are unsafe in a .223?

I've tried to research this question, but the information was so lengthy and confusingly detailed I gave up. Color me slow...

Thanks

[K.Mooneyham]

It's more complicated than that, but what you stated is a good rule of thumb.

[fickman]

That's what I go by. I'm sure somebody will come along and explain the pressures involved and a little more of the science of why.

[cubbyjg]

I hope the subject line isn't confusing, but to make my question more understandable: If a rifle is chambered for 5.56 is it also safe to shoot .223? - yes based on my research

If a different rifle states .223 without mentioning 5.56 - should .223 only be used as 5.56 pressures are unsafe in a .223?- yes based on my research. If it doesn't say 5.56, don't take the risk

I've tried to research this question, but the information was so lengthy and confusingly detailed I gave up. Color me slow...

Thanks

Depending on manufacturer and my own research, most of the prominent manufactures build the rifle to shoot 5.56. Even my dpms has 5.56 written on the barrel.

[The Annoyed Man]

In theory, case pressures are higher in 5.56 cases than in .223 cases, which makes 5.56 ammo unsafe to shoot in guns that are chambered in .223, while a 5.56 chambered rifle can manage .223 pressures just fine.

The reasons for this have to do with the arcane data of stuff like the difference in thickness of the case walls, and very tiny differences in chamber/throat/leade dimensions between the two cartridges.



Wylde chambers can shoot either, and have tolerances that are midway between the two.

Rule of thumb....the vast majority of AR15 rifles are chambered in 5.56 and will say so on the receiver/barrel. Shoot what you want in those. If your AR15 says "5.56/.223" on the receiver, you are good to go with either. If your AR15 says "Wylde" on the receiver (specific to Rock River brand rifles), you're good to go with either. If your AR15 says ".223" only on the receiver, phone the manufacturer and give them a serial number to confirm the actual chambering before you try to shoot 5.56 ammo in that rifle. If you cannot specifically confirm that rifle to be safe with NATO ammo, don't risk using it. It's not worth the potential consequences.

[Rifleman55]

On ar15s go by what is stamped on the barrel, not the lower, many rifles have been built on stripped lowers. Some lowers are stamped multi in place of the caliber designation.
Basically the biggest difference between .223 and 5.56 is the length of the throat, the 5.56 being longer.
That is like the Weatherby magnums.

[Abraham]

Great information!

Thanks everyone.

[The Annoyed Man]

On ar15s go by what is stamped on the barrel, not the lower, many rifles have been built on stripped lowers. Some lowers are stamped multi in place of the caliber designation.
Basically the biggest difference between .223 and 5.56 is the length of the throat, the 5.56 being longer.
That is like the Weatherby magnums.

True dat about the receiver stampings, but there are other differences than throat length between 5.56 and .223. NATO ammo has a thicker case wall and thicker case head, which withstand higher pressures more safely. However, that thicker metal means slightly reduced case capacity, which means that with any two compared .223 and 5.56 cartridges with identical powder charges and bullet weights, the 5.56 cartridge will generate higher chamber pressures, and that is the biggest safety issue—particularly for the handloader.

[rotor]

All good answers.
My Hornady reloading manual says...
1. 5.56 NATO SAAMI max pressure is 60,000psi and 223 Remington is 55,000 psi.
2. Chamber throat for the 223 Remington is shorter than 5.56 NATO.
3. 223 Remington may not cycle well in 5.56 NATO because of pressure degradation ( never had that in my Colt AR-15).
4. Firing 5.56 ammo in 223 Remington barrel can cause pressure related damage due to shorter throat of 223. (this can increase pressure)

So, 223 Remington in 5.56 NATO rifle OK but may not cycle ( haven't seen that) but no rifle damage.
5.56 NATO in a 223 Remington barrel potential kaboom.

Are there any AR-15 that are not 5.56 NATO on the barrel?