5.56 NATO vs .223 Remington
 

I've been recently hearing a lot of confusions that I want to be clear on. When I was at a gun store with a friend and holding an AR15, I said it's chambered in .223. My Marine buddy then say that it's also called 556, but correct me if I'm wrong. Is there a real difference between what the military uses and that NATO calls 5.56mm to that of the .223 which is by US measurements even though in the US military they still call it a 5.56mm instead of .223.

My question is what is the difference in when we have civilians with AR-15s chambered in .223 vs a military M16 chambered in 5.56mm

The .223 Remington was the cartridge from which the 5.56mm NATO was developed. The 5.56mm NATO is loaded to higher pressures, as all NATO rounds are, and are said to not be safe fired from guns specifically designated for the .223 Remington cartridge. You can fire .223 Remington rounds out of a gun designated for 5.56, as it is the higher pressured cartridge and therefore the gun built for it has higher tolerances. They are the same, but then again, they arent.

This can also be said for the .308 Winchester and the 7.62mm NATO round.

That's us civies getting the shit end of the stick, as usual. :rolleyes:

I'm pretty sure you can buy an AR-15 chambered in 5.56mm NATO, but good luck finding the ammo.

Won't any AR-15 with a steel reciever (not alloy crap they usually make them with) withstand higher pressure? My Bushmaster has a steel reciever, so I'm wondering.

Actually the original models were all manufactured with high strength Aluminum recievers, and they took the 5.56mm NATO rounds, but as we've learned before, the reciever can be made of pretty much anything, (like plastic or wood). The upper should be fully constructed of steel, and almost always is. A steel reciever would probably make the gun a bit tougher, but add some weight as well.

Yeah, my Bushmaster is a carbine and is just as heavy as a full length Colt HBAR, because the Bushmaster is better made of more solid metal.

Actually, the difference is in the leade (the space between the end of the cartridge and where the rifling starts. It's somewhat longer in the 5.56mm NATO, which can lead to reduced accuracy when firing some .223 cartridges out of a NATO chamber, or reliability when firing NATO ammo out of a match-grade .223 chamber.

NATO allows a different max pressure than SAAMI, but that's got more to do with different methods of measuring than anything - the European proof houses give the same max pressure for both. Military cartridges have thicker brass since they're more concerned with reliability than reloadability. SS109 or Mk.262 could potentially lead to higher pressure in a .223-spec chamber, but not so much that it's gonna blow up in your face.

Thanks Nyles for explaining the difference between .223 Rem and 5.56 NATO.

We had a PD bring in their Bushmaster built carbines with stainless steel barrels as they would not function on Full Auto firing 5.56 NATO. We had to go in with a 5.56 NATO chamber reamer and give them the correct chamber for the cartridge. Once that was done they worked perfect in Full Auto mode.

Did you check that receiver with a magnet at the rear were the lug for the take down pins? I wondering as the only steel receiver I have seen is on a .308 model AR and it was fully machined.

The receivers used by Colt, FN, LMT, S&W, DPMS, Armalite, Bushmaster and others are 7075 forgings which is the exact same material used in jet aircraft including the latest fighters like the F-22 and F-35.