223 in a 556

[Turfweazel]

I am going to be getting a new gun in .223 soon. This is my first gun in the caliber so I am kind of new to it and don't want to hurt my new beauty. I have seen some people say you can interchange 223 and 556 and some say you can't. I thought I saw a post about this at one point that the two rounds were different sizes by just a little. I did a search but didn't come up with much. Any help would be great to clear this up for me thank you.

 

[Cameramonkey]

If the gun is chambered in 5.56, you can shoot either. If its chambered in .223 you can only use that. (but always check the owners manual to verify)

The reason is 5.56 rounds are a higher pressure round, and although they may fit into a .223 gun, the chamber might not be designed strong enough for the extra stress and could cause damage to the gun.

 

[Scratcher]

If the gun is chambered in 5.56, you can shoot either. If its chambered in .223 you can only use that. (but always check the owners manual to verify)

The reason is 5.56 rounds are a higher pressure round, and although they may fit into a .223 gun, the chamber might not be designed strong enough for the extra stress and could cause damage to the gun.

About sums it up

 

[maverick5990]

I am going to be getting a new gun in .223 soon. This is my first gun in the caliber so I am kind of new to it and don't want to hurt my new beauty. I have seen some people say you can interchange 223 and 556 and some say you can't. I thought I saw a post about this at one point that the two rounds were different sizes by just a little. I did a search but didn't come up with much. Any help would be great to clear this up for me thank you.

The lower will be stamped with either 5.56 or 2.23 close to the manufacturer mark.

 

[Mgderf]

The lower will be stamped with either 5.56 or 2.23 close to the manufacturer mark.

If it's an AR platform, and the stamp on the lower is meaningless. Look at the stamp on the barrel in the case of an AR15 style rifle.

If you're talking about a bolt gun in .223 Rem, ONLY fire .223 in it!

 

[HoughMade]

Barrel, usually not lower. Standard AR lowers can be used with a myriad of rounds.

 

[sloughfoot]

If the gun is chambered in 5.56, you can shoot either. If its chambered in .223 you can only use that. (but always check the owners manual to verify)

The reason is 5.56 rounds are a higher pressure round, and although they may fit into a .223 gun, the chamber might not be designed strong enough for the extra stress and could cause damage to the gun.

Not true unless you specify that the 5.56 of which you speak is 5.56 NATO. 5.56 Mil-Spec is the 55 grain fmjbt used from the 1960's to the present. It is no more pressure than any 55grain commercial ammo. It is totally safe in a 223 chamber. I have 45 years experience with it.

OP, 5.56 NATO should never be fired out of a 223 chamber. The green tip bullet is too long and is very high pressure.

 

[sloughfoot]

Thanks for the reps. PM with your email if you want to read the 1988 NRA article that discusses the "new" 5.56 NATO round. Also, the changes that resulted in the M16A2 to use the new round. I will email it to you.

Sadly, many writers obscure the differences in their writings on the subject. It's always there. Just buried in the text.

The differences are very clear to anyone who shot the M16A1 and 223 before 1988.

 

[Cameramonkey]

The lower will be stamped with either 5.56 or 2.23 close to the manufacturer mark.

Not true unless you specify that the 5.56 of which you speak is 5.56 NATO. 5.56 Mil-Spec is the 55 grain fmjbt used from the 1960's to the present. It is no more pressure than any 55grain commercial ammo. It is totally safe in a 223 chamber. I have 45 years experience with it.

OP, 5.56 NATO should never be fired out of a 223 chamber. The green tip bullet is too long and is very high pressure.

Actually, as a blanket statement of "will a 223 handle a 556" my statement is correct. Thats the whole point of the 5.56 stamp... to show that the chamber can handle the 5.56 NATO round. So you are saying there are 5.56 stamped barrels that are actually OK for 5.56 but NOT OK for 5.56 NATO? I find that difficult to swallow. Seems like a lawsuit waiting to happen to me.

 

[sloughfoot]

Yes. The M16A1 and the early AR15 equivelants were indeed marked 5.56. Their chambers were large to accommodate full auto fire (in the M16) therefore still safe to fire 5.56 NATO. What made the new 5.56 ammo unsuitable was barrel twist. The early rifles were 1X12 twist. Too slow to stabilize the 62 grain penetrator that is in the 5.56 NATO.

Modern AR barrels are marked 5.56 NATO. At least all of them I have seen. I have never seen a modern barrel in 7, 8, or 9 twist without NATO right after the 5.56.

Aside from pressure issues, most 223 boltguns are not compatible because of their slow twist rate. But the 12 twist 223 boltgun shoots military surplus or commercial 55 grain fmj without issues.

 

[Cameramonkey]

I think we are talking past each other. I should correct my initial statement. "if it is marked 5.56 NATO (as they all are in modern firearms) you can shoot either".

I havent seen anything NOT marked as NATO, hence my intial omission.

 

[sloughfoot]

And of course, since the M193 55gr ammo was never adopted by NATO, it is just 5.56 not 5.56 NATO. That is why precise speaking is important on this issue. Sadly, too many pro writers have muddied the issue by not being precise in their writing.

In order for NATO to adopt the M855 62 grain penetrator, they pushed the heavier longer bullet as fast, or a little faster than the 55. Hence, the higher pressure and need for the long leade.

M193 is 5.56

M855 is 5.56 NATO

All Mil-Surp and commercial 55 gr is exactly the same as M193. Pressures and velocities are the same. I have testing to prove that too.

 

[Robjps]

Ruger mini 14 and some colts are stamped 223 but can handle 556 refer to the owners manual.

 

[ViperJock]

Ruger mini 14 and some colts are stamped 223 but can handle 556 refer to the owners manual.

To further confuse the issue; enter 223 Wylde.

 

[Leo]

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[Leo]

In the 1970's there were TWO reamers in the Cylmer catalog, .223 and 5,56 (NATO maybe not the right name). I have not looked them up lately, but last I looked, there were 10 or 12 standard pattern chamber reamers. All but two of them are compatable with either round. The pressure issue is related to a chambering problem where there is no free bore in the leede. There is not such thing as a "high pressure" barrel extension or bolt. As long as the bullet major ogive diameter is not jammed into the throat, the initial destructive pressure spike does not happen. WHen the stubbier bullet nose is jammed into the leade, the initial pressure peaks way higher, resulting is pressure way above that. Sort of like blowing up an AR with magnum pistol powder instead of medium rifle powder.

Except for one old Remington bolt action, all the barrels I have ever chamber cast and measured up have been cut with a reamer pattern that is a hybred that will accomodate either bullet shape, no matter what is stamped on the barrel. As a rule of thumb, if you do not have the ability to measure up the chamber, it is best to count on what ever is stamped on the barrel.

I believe all the technical reports from SAMMI as correct with the chamber dimensions they qoute. I have not seen barrels chambered in the old pattern in a long time. I think the rifle and barrel manufacturers are trying to avoid safety issues by using the more generous reamers.

 

[sloughfoot]

Leo my friend. There could not have been a 5.56 NATO reamer in the 1970's. There certainly was a 5.56 reamer, but the only cartridge available at the time utilized the 55 grain and the lighter 40 grain varmint bullets. The 5.56 and the .223 reamer were so close to each other in 1975 that the differences were ignored.

Even the 69 grain bullet for the AR was not introduced until the mid 1980's by Sierra. Because by then, everybody was starting to realize the potential of the mouse gun with a faster twist than 12.

NATO did not adopt the 5.56 until it passed the helmet penetration at 300 yards test with the M855 steel core penetrator in 1981 or so. NATO ignored the M193 55 grain loads and still do to this day. Or was it 600 yards? Crap now I don't remember. But I do know that until the little cartridge could do it, NATO had no interest in it. 7.62X51 was king of the hill until that point.

And yes, chambers are generous because the gun manufacturers know that someone will fire the wrong ammo through the tube. That is why twist rate is the more limiting factor than exactly what chamber has been cut into the barrel.

 

[Leo]

OK, Since I do not have 40 year old paper work, there was two. Lets call it Commercial and military, I surely cannot remember if it stated "NATO". I bought the reamer, set back my .222 Rem barrel and rechambered it in .223 around 1978. There was also a .222 Mag at that time, but I figured that the .223 would be more common. My goal was to hotrod the little .222 without having to fire form Ackley Improved cases. Speer made a flat based 70 grain bullet, but I never got it to shoot right because of twist issues. I do not remember if Sierra made the 69 grain then, as I was interested in varmint hunting. It would shoot 50 grain bullets really well. Another experiment that did not turn out. Such is the life of experimenters.