556 so you can use both 556 and 223
223 if you only plan to shoot 223
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If you buy 556 you can only shoot 556 but if you buy 223, you can shoot either round. It’s not advisable though, as the 556 is a hotter round creating more pressure in the chamber.
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It is, and always will be, safe to shoot .223 Rem. ammunition in a chamber marked for 5.56 NATO. Commit that idea to memory, and you’ll never get in trouble. The pressures that a 5.56 NATO cartridge can generate are too high for the .223 Rem. chamber, and that is based primarily on the leade dimensions. If you feel that the ability to shoot 5.56 NATO ammunition out of your .223 Rem.-chambered rifle is paramount, take that rifle to a competent gunsmith to have the chamber reamed out to handle 5.56 NATO ammunition.
https://www.shootingillustrated.com/articles/2018/7/28/556-nato-vs-223-rem-whats-the-difference/
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Thanks for that…I got it backwards…
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Got that backwards, 556 can shoot 223 and 556.
If you get 223, sure you likely could shoot some 556 but it was never meant for the higher 556 pressure and you risk damage to your firearm and probably catastrophic failure eventually.
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5.56 is the safe route to go.
The best of both worlds is the .223 wylde but in reality the gun will be more accurate than the shooter so pressure wise 5.56 is the safe route
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5.56 is interchangeable with 223 but 223 is not interchangeable with 5.56
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Similar rules here but we have to use straight wall cartridge… so My brother-in-law and I built a 450 bushmaster at pistol
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