5.56x45 vs 223 rem

[hyperdog]

Can someone please explain to me the difference?

I am looking to get a SCAR 16s and it says chambered in the 5.56 nato /223 rem. Does this mean it will take both bullets? If so then why do the sell both bullets?

Thanks for helping out a rifle noob.

[localgirl]

Yes, if the rifle says it is chambered for both, it will take both.

The rounds are practically the same, but some barrels are more exact than others.

For example, the military-spec AR-15 is chambered for the 5.56, and though you might be able to stuff a .223 in there, it can cause problems.

Different but similar calibers usually come about as the result of military trials, where they try to fine tune the weapon, plus they want a caliber specific to NATO standards.

You'll find civilian-grade weapons are often more forgiving.

[Horkos]

Look here : http://en.m.wikipedia.org/wiki/5.56x45mm_NATO

From above link :
"Using commercial .223 Remington cartridges in a 5.56*mm NATO chambered rifle should work reliably, but generally will not be as accurate as when fired from a .223 Remington chambered gun due to the longer leade.[15] Using 5.56*mm NATO mil-spec cartridges (such as the M855) in a .223 Remington chambered rifle can lead to excessive wear and stress on the rifle and even be unsafe, and SAAMI recommends against the practice.[16][17] Some commercial rifles marked as ".223 Remington" are in fact suited for 5.56*mm NATO, such as many commercial AR-15 variants and the Ruger Mini-14 (marked ".223 cal"), but the manufacturer should always be consulted to verify that this is acceptable before attempting it, and signs of excessive pressure (such as flattening or gas staining of the primers) should be looked for in the initial testing with 5.56*mm NATO ammunition.[18"

[Tony Quilici]

hyperdog, read over this article:

5.56×45mm NATO - Wikipedia, the free encyclopedia

The thing that you need to know and remember is that a rifle/carbine chambered for 5.56mm NATO will fire not only the round intended for it, but also .223 Remington. However, a rifle/carbine chambered for .223 Rem, WILL NOT fire 5.56mm NATO. Also, the rifle twist of the bore will determine what grain size of bullet that can be fired as well. I own an Armalite M-15 Carbine and I have fired both 5.56mm and .223 Rem with no problems. The 5.56mm however gives me tighter groups, but not by much. Talking shooting 2.5 MOA at 250 meters with .223 Rem and then 2 MOA with 5.56mm, open sights.

[medic72]

What this has to do with is the "chamber pressure". A rifle chambered for 5.56mm WILL safely fire the "military" rounds, while one chambered in .223rem can not. What happens is the "throat" in the chamber is different, and then you have an increase in pressure, which may result in failure. I say if in doubt call the manufacturer. They will be able to tell you (I called bushmaster), with that said go with a weapon that says 5.56mm because it can shoot the .223 rem but not reversed.
O

[Widowerks]

The 5.56 developes aprox. 10.000 psi more chamber pressure than the commercial .223 rem. cartridge - NOT good for a bolt action.The 5.56 NATO rnd. has a thicker case web,walls and slightly different dimensions also but will chamber in a .223 rem. chamber. That leade mentioned is the real trick, as the NATO rnd. has the bullet set out farther than the .223 rem. cartridge and needs the leade to properly engage the rifleing
Horkos stated most of it correctly. The excess pressure can actually bend the bolt and it also causes a semi auto to 'slam' against the bolt stop eventually leading to a deformed action, which is why there are recoil buffers sold to reduce that problem and they require constant replacement as well.

[jcmorris71]

The above link in wright on. I'm only a Navy Small Arms and Crew Served weapons instructor, that said, some rifles will take one or the other or both. One just has to know which one it calls for and you have that covered. It is basically a military designation and a civilian designation. Like .308 Win and 7.62x51 NATO.

[Mud pup P]

Just buy a mini 14, it shoot .223 / 5.56 and .222 Remington ;)

[Usa007]

.223 and 5.56 I have used only 5.56 in my AR but want to try .223 should I expect a difference in accuracy between both calibers?

[6shootercarry]

.223 and 5.56 I have used only 5.56 in my AR but want to try .223 should I expect a difference in accuracy between both calibers?

That is really a function of the twist rate of the barrel. More aggressive twist rates (1:7) tend to make heavier bullets go more accurately to the target. 65-80 grain works nice with 1:7... lesser twist rates tend to send lighter bullets to target with more accuracy... 1:9 or 1:11 work nice with 45-55 grain bullets..

Twist rate or ratio. First number = number of revolutions of projectile, 2nd number = inches of barrel projectile must travel through in order to make the single revolution. Smaller second number = more aggressive twist rate.

The difference in the cartridge is kinda small. Slightly thicker cases on the 5.56 NATO ammo. NATO ammo is loaded to higher chamber pressure 223 Rem is loaded to SAAMI specs (56,000 to 57,000 psi) NATO rating for the same cartridge is higher 62,000 or just above that...

The leade in the chamber is the distance from the case throat to where the bullet will encounter the lands of the riffling at the narrowest point!! SAAMI spec chambers have shorter leade. NATO spec chambers have longer leade.. Smaller chamber leade = higher pressure.. Most barrels and chamber designs are proof tested, usually to 125% rating. A steady diet of over pressure rounds is not recommended..

Chambers: that all-important point where everything starts | Guns Magazine | Find Articles at BNET

More to read...

So look at the barrel on your AR and see what the twist rate is then try some 3-5 shot groups with differing bullet weights and configurations FMJ vs hollow point. Do this using a bench rest to remove human error when shooting. Try and choose a calm day for the test. Kinda the difference between zero and true zero. Another major way to mess with accuracy is cleaning the barrel from the muzzle or crown end... Damage the muzzle crown and accuracy will suffer. It's the last part of the barrel that has an effect on trajectory.

My 2 pennies..