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Posted: 5/6/2008 2:36:07 AM EDT
| Please explain, I found a warning on a case of federal xm193 "not for use in rifles chambered in .223. What exactly is the difference? |
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What you don't read?????? 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 and should have no trouble firing hot 5.56 ammunition. 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 or leade 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 commercial AR manufacturers use the tighter ".223" (i.e., SAAMI-spec and often labeled ".223" or ".223 Remington") chamber, which provides for increased accuracy but, in self-loading rifles, less cycling reliability, especially with hot-loaded military ammo. A few 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, if any, on the barrel, but always check with the manufacturer to be sure. Typical Colt Mil-Spec-type markings: C MP 5.56 NATO 1/7 Typical Bushmaster markings: B MP 5.56 NATO 1/9 HBAR DPMS marks their barrels ".223", though they actually have 5.56 chambers. Olympic Arms marks their barrels with "556", with some additionally marked "SS" or "SUM." This marking is used on all barrels, even older barrels that used .223 chambers and current target models that also use .223 chambers. Non-target barrels made since 2001 should have 5.56 chambers. Armalite typically doesn't mark their barrels. A2 and A4 models had .223 chambers until mid-2001, and have used 5.56 chambers since. The (t) models use .223 match chambers. Rock River Arms uses the Wylde chamber specs on most rifles, and does not mark their barrels. Most other AR manufacturers' barrels are unmarked, and chamber dimensions are unknown. mike eta - there's a detail and other information there (in the Ammo Oracle) that would be helpful to ya - shame you passed on the advise I gave ya in the other thread......  |
Sorry, was only half awake and half reading. Thanks for your trouble. Excellent article tho. |
My dpms is definitely marked 5.56. I guess mine is just a fluke. |
which is right? I just got it in the mail, lol.
That's a relatively recent change. Parts of the Ammo Oracle are 6 years or more old, and AR and ammo manufacturing is constantly changing. -Troy |
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