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45JMB 03-02-2013 04:18 AM

I know that a M16 fires the 5.56x45 but AR15 fires the 5.56x39 right? Which is known as .223

unclebear 03-02-2013 05:05 AM

no, I don't know a whole lot about AR's but they there are some with a stamp that says 5.56X45 and some that say 223 really they pretty much the same round, They"re are some small differences in measurement just like 7.62X51 to 308.

The AK rounds are 7.62X39 (AKM) and 5.45X39 (AK74)

Apex-Predator 03-02-2013 05:16 AM

Yeah there is no 5.56x39, or if there is it is some funky wildcat cartridge.

BULLET9992 03-02-2013 05:18 AM

The difference of the .223 & 5.56x45mm are negligible or even non existent. When the 556 was originally designed it may have had higher chamber pressure but with modern powder some 223 ammo out performs the 556. The difference is how it's measured. The .223 Remington has a .223 inch wide bullet, that's where it gets the name. The 556 has a 5.56mm wide bullet (same as .223") & a 45mm leangth casing. The 556 NATO is only different in the way that it is a metricly measured round & that's it. Allowing it to be a world wide recognised ammunition size & meeting NATO requirements. They'll both feed & fire properly out of either a 223 or 556 gun.

BULLET9992 03-02-2013 05:22 AM

Unless it's military ammo, then the 556 ammunition may have higher chamber pressures. Typically for any specialty ammo.

45JMB 03-02-2013 05:25 AM

Thanks a lot guys. It's just because people said that the .223 and 5.56.39 Are totally different rounds.

Apex-Predator 03-02-2013 05:53 AM

5.56x45 IS different then 223, just not very different. They have the same outside dimensions but the thickness of the brass and pressure are different. Technically you are not supposed to fire 5.56x45 out of a 223 but you can fire 223 out of a 5.56x45 since the 5.56 is a higher pressure round.

BULLET9992 03-02-2013 06:42 AM

Depends on what 556 you get. The vast majority have no differences. If I had to choose between a 223 ar & a mil spec 556. I'd go for the 556 even if it's a little more expensive. They're typically better made. In a bolt gun your set because they're designed for high pressure ammo.

Jagermeister 03-02-2013 07:01 AM

Mil Spec ammo runs pretty hot, so you shoot higher then say a hunting round. Not as good quality then hunting ammo. Also, I noticed that my .308 hunting round is slower but better quality and very accurate.. The NATO/mil spec shoots about 2.5 to 3 inches higher at 100 meters and grouping can be questionable per box. The mil ammo also makes the rifle barrel really dirty in a short period of time. The NATO rounds is a third of the price though. If you are using the gun for self defense and target shooting go with mil spec. I would not use "NATO" rounds for hunting or competition. I am also too lazy to continually adjust scope between ammo.

mchoitz 03-02-2013 01:18 PM

It's not recommended to shoot 5.56 out of a .223 barrel but you can shoot a .223 out of a 5.56 barrel no problem

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