# .223/5.56 explaned



## Smitty901 (Nov 16, 2012)

It seems from time to time we must address the differences. Between .223 and 5.56. Without going into a year long study and to keep it simple.
The .223 is not a 22 it is a .223 . It started out as a Remington .223 born from the .222. it was adopted for the M16 Military platform. After some research the Military settled on a 20 inch barrel with a 1 in 12 twist using the .223 in a 55gr round The M16. Regardless of the myth and folk lore the round worked.
Over time the Military wanted to make the M16 smaller and even lighter that gave birth to the M4 pretty much what you now call a AR15.
To increase the .223 penetration and to make the round more effective in a 16 inch barrel the Military switched to the 5.56 .
The difference is pressure rating. The 5.56 was designed to fire at higher pressure. That is why you can fire .223 in a 5.56 but it is not commonly recommend to fire 5.56 in a .223. There are exceptions.
The .223 55gr round did not work well in the 5.56 16 inch barrel. They tried several barrel twist rates and settled on the 1 in 7. Also the 55gr round was not suited for a 16 inch 1 in 7. They settled on a 62 gr and latter did use some 77gr. Another story.
When you fire a .223 55gr round in a 5.56 16 inch 1 in 7 they work fine. However some loss in accuracy is seem and the farther out the worst it gets. Also the lighter round fired from that weapon fails as a man stopped.
The long and short of this the Modern AR15 with a 16 inch barrels are not designed for the .223 55gr it is meant for a 5.56 with a 62gr or slightly heavier round.
Now we can post pages of history and a whole book of studies but If you do a bit of home work the basics are covered above. getting into 1 in 8 and 1 in 9 twist just confuses the issues but does not change things much. Same the with the .223 20 inch in a 1 in 14 twist.
The M4 was never designed to be a sniper rifle . It was meant to kill at close range and out to 500 meters with basic skills and even farther with some training.
To keep things simple your AR15 preforms best over all with 5.56 62 gr.
Save a few cents a round buying .223 55 gr rounds will not be such a good deal when you need them to do the job.


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## Rwurbanwildlife (Nov 9, 2012)

So is a .22 magnum a .22 or a .223??


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## Smitty901 (Nov 16, 2012)

Rwurbanwildlife said:


> So is a .22 magnum a .22 or a .223??


 The .222 Remington, and the .222 Remington Magnum were predecessors to the .223 Remington They were center fire . The Remington .222 is not the .22 you are use to. But do not confuse a the M16 and AR round with a .22 or a .222. The Remington .222 round is not commonly found anymore.
Also the .223 needed to stay supersonic to 500 yard the .222 could not even come close to that.

Remington .222


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## Boss Dog (Feb 8, 2013)

That's about as good as I've seen it put Smitty.


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## keith9365 (Apr 23, 2014)

Informative read. I fired 5.56 nato in the military but never in combat.


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## Diver (Nov 22, 2014)

While what Smitty said is right on, there are still .223 rifles on the market. You need to know what you have.


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## Chipper (Dec 22, 2012)

Simpler explanation. 556 is a military cartridge loaded "hotter" to a higher pressure than the 223. An attempt to get better performance out of a varmint hunting round for combat. Basically the same round but with the higher pressure you shouldn't shoot the 556 round in a gun designed and rated for the lower pressure 223.

Your not risking anything by using the lower pressure 223 in your 556. As the 556 is designed for the higher pressure military round.


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## keith9365 (Apr 23, 2014)

I know everybody rolls their eyes and says BS when you hear "I know a guy who knew a guy who saw a guy….." But I saw an Olympic Arms A1 style AR15 blow up when the the shooter popped off NATO 62gr green tip.


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## dannydefense (Oct 9, 2013)

keith9365 said:


> I know everybody rolls their eyes and says BS when you hear "I know a guy who knew a guy who saw a guy&#8230;.." But I saw an Olympic Arms A1 style AR15 blow up when the the shooter popped off NATO 62gr green tip.


That wasn't because it was chambered in .223, that's because it was an Oly. Could have happened with any round.


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## Smitty901 (Nov 16, 2012)

Diver said:


> While what Smitty said is right on, there are still .223 rifles on the market. You need to know what you have.


 Yes and I own a couple Ruger .223 model 77's fine rifles.
Also Ruger has stated that the mini 14's that are stamped .223 will fire 5.56. However I would check by serial number.
I did not want to confuse thing with the other transition custom chambers that were around I figure if you get into that we need another thread.
Many are marked both and some that are marked .223 are both even when not marked.
I have known of many that fire 5.56 in weapons marked .223 and not had an issue I however can not public make that call.
One way you will know is if you shoot a 5.56 in one marked .223 and have issue ejecting the round I would not do it again.


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