The information is correct with respect to .223 vs 5.56x45, but ONLY with regards to pressure.
Milspec 5.56x45 is HOTTER than SAAMI spec for .223. As such, if you have a marginal rifle that is designed for .223, don't use USGI ammo in it.
BUT, AR-15's are built to handle USGI pressures.
The only thing to do with "chambering" is that a tight "match" chamber made close to .223 specs will be too tight for your average USGI spec ammo. Yes, it will mostly chamber and fire. That is, until you let the system get dirty, or you hit an oddball round that is sized incorrectly. Then you might get a slamfire, or other problem.
This is a borderline issue. For the AR-15, it is a NON issue except as mentioned. The AR-15 barrels and actions are built to handle hotter than SAAMI spec, specficially hot loads for M193 and SS109.
Maybe I missed something here, but Miltary ball ammo is not loaded to a higher pressure. Military ball is usally 20% less than shelf ammo. Just like the .308`s, HK, FN/FAL`s and the rest show specs for 2450-2750fps....firing a 147grn projectile. This is a much lower pressure that shelf ammo and most will void warranty,if found that you used reloads or shelf ammo, and not Mil-Spec. The M1a by Springfield states the same thing and if you choose to shoot hotter reloads or store brands, you must add a gas regulator or you will cause undue wear on it. What am I missing??? If you fire commercial grade .223 in your AR15, it will cause premature wear.....if you have not upgraded the buffer or added a gas regulator, go to a match and you will see (unless stock rifle) Hi-Power shooters using hot reloads with adjustable gas systems in their rifles. LTS
From the ammo oracle--http://www.ammo-oracle.com/#diff
Q. What is the difference between 5.56×45mm and .223 Remington ammo?
In the 1950's, the US military adopted the metric system of measurement and uses metric measurements to describe ammo. However, the US commercial ammo market typically used the English "caliber" measurements when describing ammo. "Caliber" is a shorthand way of saying "hundredths (or thousandths) of an inch." For example, a fifty caliber projectile is approximately fifty one-hundredths (.50) of an inch and a 357 caliber projectile is approximately three-hundred and fifty-seven thousandths (.357) of an inch. Dimensionally, 5.56 and .223 ammo are identical, though military 5.56 ammo is typically loaded to higher pressures and velocities than commercial ammo and may, in guns with extremely tight "match" .223 chambers, be unsafe to fire.
The chambers for .223 and 5.56 weapons are not the same either. Though the AR15 design provides an extremely strong action, high pressure signs on the brass and primers, extraction failures and cycling problems may be seen when firing hot 5.56 ammo in .223-chambered rifles. Military M16s and AR15s from Colt, Bushmaster, FN, DPMS, and some others have the M16-spec chamber with a longer throat and should have no trouble firing hot 5.56 ammunition. The big difference between the two chambers is in the chamber dimensions. Military M16s have slightly more headspace and have a longer throat area, compared to the SAAMI .223 chamber spec, which was originally designed for bolt-action rifles. Commercial SAAMI-specification .223 chambers have a much shorter throat, a smaller diameter bullet seat and less freebore than the military chamber. Shooting 5.56 mil-spec ammo in a SAAMI-specification chamber can increase pressure dramatically, up to an additional 15,000 psi or more.
The military chamber is often referred to as a "5.56 NATO" chamber, as that is what is usually stamped on military barrels. Some AR manufacturers use the tighter ".223" (i.e., SAAMI-spec and often labeled ".223" or ".223 Remington") chamber, which tends to give you more accuracy but, in self-loading rifles, less reliability, especially with hot-loaded military ammo. Some AR manufacturers use an in-between chamber spec, such as the Wylde chamber. Many mis-mark their barrels too, which further complicates things. You can generally tell what sort of chamber you are dealing with by the markings on the weapon, but always check with the manufacturer to be sure.
Q. Which should I be looking for in an AR15, 5.56 NATO or .223 Remington chambers?
This is really a matter of the role for which you plan to use your AR. .223 Remington chambers will give you slightly better accuracy, which is important for a match or varmint rifle. Any loss of feeding and cycling reliability and the restriction against shooting military ammo isn't as important as the accuracy gains for a rifle used in these roles, because for these rifles, accuracy is everything. People who just want to plink or who plan to shoot military ammo (such as most of the cheap surplus ammo available), and especially those who may use their AR as a weapon, should choose 5.56 chambers.
Consult the oracle-it should answer most of your questions.
i may not be the total geek for pressures, loads, etc, but i've shot XM193, American Eagle, PMC, and the southa african milsurp ammo through my AR. they're all pretty lame ... until that XM193 chambers up and KA BAAAAAM that stuff lights up!! always makes my day to shoot that stuff!!!
I just visited Rock Rivers site & they have 2 chamberings offered:
223/5.56 NATO, This is the standard A2 chamber.
223 Wylde, This is a chamber that kinda splits the difference between a 223 chamber & a 5.56 NATO or A2 chamber.
this is an email i sent to Bushmaster regarding their DCM barrels..
hope this helps.
Your catalog list ALL Bushmaster barrels are chambered for 5.56Nato, that it is safe to shoot .223 Remington. But on page 13 of your 2003 catalog.. the DCM rifle is described as having a SAAMI spec barrel. Doesnt say 5.56 or .223, just SAAMI spec. I assume SAAMI is 223 remington. IF so, is it safe to shoot 5.56 thru my DCM???? 2nd question. Your catalog states 1x9 barrel will stabilize up to 75gr ammo. 1x8 DCM will stabilize heavier bullets for competition. Well, how much heavier???
The DCM barrels have a special hybrid type of chamber where it has the tighter SAAMI Spec headspacing from the shoulder of the chamber to the bolt face it does have a longer leade or throat than a .223 chamber so that 5.56mm ammunition can be used.
The 1 X 8 twist will stabilize bullets up to 80 grains which must be single fired as they are too long to fit the magazine.