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Old 02-17-2009, 07:37 AM
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Are these rounds interchangeable in the M&P 15 and similar ARs?
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Old 02-17-2009, 07:37 AM
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Are these rounds interchangeable in the M&P 15 and similar ARs?
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Old 02-17-2009, 07:55 AM
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AR-15's are typically chambered for 5.56. You can safely fire .223 ammo in them, however .223 is generally not loaded to as high a pressure (velocity will be less), and depending on the rate of twist of the barrel some bullets, typically lighter varmint rounds, may not shoot accurately.

More info here.
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Old 02-17-2009, 08:34 AM
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Generally speaking it is Ok to fire .223 in weapons chambered for 5.56 but not 5.56 in weapons chambered in .223.
Think shooting .38 special in a .357 magnum.
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Old 02-17-2009, 08:45 AM
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Chamber drawings:
JGS used to make a fantastic 3 ring binder book full of heavy stock paper chamber drawings. Well worth the bucks for any avid gun person. Don't know if they are still available, but mine has been invaluable over the years. Got it sometime in mid 90's or so. There is a difference and the nato chamber is looser for reliable semi auto feed and ammunition manufacturer tolerance reasons and if you want any specifics e-mail me and I'll give them to you.
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Old 02-17-2009, 09:28 AM
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I too have heard that it is not good to use 5.56 NATO in a .223 marked chamber but it is OK to use either in a 5.56 marked gun. I have a M&P 15T and have used both rounds with no problems. The M&P models tend to have a slower twist so they stabalize the lighter bullets better. The heavier bullets will work, they just aren't as accurate (in general).
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Old 02-17-2009, 11:42 AM
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Thanks guys.
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Old 02-18-2009, 12:23 PM
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These are two different rounds. There is some good information out about this. Check out the recent articles in SWAT by Ned Christiansen with regard to this. Also, a fair number of makes mark their chambers 5.56x45 but are not correct. When I was at the Dean Caputo class in Four Oaks NC last fall, more than a few chambers were measured then reamed with Ned's chamber reamer; all needed it badly. There are a couple of places you can get "the chart" by Rob_S, like m4carbine.net.
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Old 02-18-2009, 02:24 PM
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There are two issues here: chamber design and ammmo specifications.

The 5.56 chamber is, ah, generous in certain areas to ensure function in full auto weapons under sustained fire conditions. To the point that some chambers which will pass a 5.56 mm chamber gauge will fail a .223 no-go gauge.

The ammo spec difference is due to the 5.56 mm having a velocity requirement for a 20 inch barrel at 78 feet which is higher than that generally produced by .223 with comparable bullets/barrel length. This requires a higher than SAAMI specification pressure.
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Old 02-19-2009, 10:17 AM
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An interesting question.

I just bought some ammo, federal 5.56 XM193BK, which according to the research I've done, is higher pressure than .223 and should not be fired in a rifle chambered for .223.

I consulted my Hornady 7th, which has data for both .223 and AR15. They call it .223 service rifle, not 5.56. The AR15 data is LOWER than the .223 data.

I was hoping to shoot it in both my AR15 and Winchester M70 (.223), but I'm a bit hesitant to shoot it in my M70 now.
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Old 02-24-2009, 12:19 AM
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Quote:
Originally posted by Lucky Derby:
Generally speaking it is Ok to fire .223 in weapons chambered for 5.56 but not 5.56 in weapons chambered in .223.
Well there-ya-go.....
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Old 02-24-2009, 10:09 PM
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Quote:
Originally posted by johngalt:
An interesting question.

I just bought some ammo, federal 5.56 XM193BK, which according to the research I've done, is higher pressure than .223 and should not be fired in a rifle chambered for .223.
*
Gotta be careful with the "X" designator. That means it failed final inspection, and according to persons more knowledgeable than I, for the last couple years the failures are often pressure related.
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Old 02-25-2009, 06:38 PM
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Quote:
Originally posted by Doug M.:
Gotta be careful with the "X" designator. That means it failed final inspection, and according to persons more knowledgeable than I, for the last couple years the failures are often pressure related.
My understanding is that the "X" indicates commercial (non-military) ammo, and has nothing whatsoever to do with having passed or failed inspection. XM193 is loaded to the same specs as military M193 (and may even be from the same production run) but is packaged and sold through civilian channels. The suffixes (A, C, BK, etc.) indicate packaging differences, such as type of box, stripper clips, etc.

Do you really think Federal would sell "XM193" ammo from the Lake City plant that was defective, especially if the defect was pressure-related?!?
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Old 02-25-2009, 07:56 PM
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My recollection may be poor, but that is in fact my understanding.
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Old 02-27-2009, 05:17 PM
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Interesting post I thought the cartridges where one and the same. My Speer #10 reloading manual does not mention them seperately.
Wikipedia has this to say.

5.56mm NATO versus .223 Remington

While the 5.56mm NATO and .223 Remington cartridges and chamberings are very similar, they are not identical.

Military cases are generally made from thicker brass than commercial cases; this reduces the powder capacity (an important consideration for handloaders[4]), and the NATO specification allows a higher chamber pressure. NATO EPVAT test barrels made for 5.56mm NATO measure chamber pressure at the case mouth, as opposed to the location used by the United States civil standards organization SAAMI. The piezoelectric sensors or transducers NATO and SAAMI use to conduct the actual pressure measurements also differ. This difference in measurement method accounts for upwards of 137.9 MPa (20,000 psi) difference in pressure measurements. This means the NATO EPVAT maximum service pressure of 430 MPa (62,366 psi) for 5.56mm NATO, is reduced by SAAMI to 379.21 MPa (55,000 psi) for .223 Remington.[5] In contrast to SAAMI, the other main civil standards organization C.I.P. defines the maximum service and proof test pressures of the .223 Remington cartridge equal to the 5.56mm NATO.

The 5.56mm NATO chambering, known as a NATO or mil-spec chamber, has a longer leade, which is the distance between the mouth of the cartridge and the point at which the rifling engages the bullet. The .223 Remington chambering, known as SAAMI chamber, is allowed to have a shorter leade, and is only required to be proof tested to the lower SAAMI chamber pressure. To address these issues, various proprietary chambers exist, such as the Wylde chamber (Rock River Arms)[6] or the Armalite chamber, which are designed to handle both 5.56mm NATO and .223 Remington equally well. The dimensions and leade of the .223 Remington minimum C.I.P. chamber also differ from the 5.56mm NATO chamber specification.

Using commercial .223 Remington cartridges in a 5.56mm 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.[7] Using 5.56mm 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 the SAAMI recommends against the practice.[8] Some commercial rifles marked as ".223 Remington" are in fact suited for 5.56mm NATO, such as many commercial AR-15 variants and the Ruger Mini-14, 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 5.56mm NATO ammunition.

Anyway interesting topic.

Troy
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Old 02-28-2009, 12:09 PM
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I have a fairly new Ruger Mini 14. The literature that came with the gun specifically states that it is safe to fire either .223 or 5.56 ammo in it. It is marked .223. I think this may be more of an issue with bolt actions with tight chambers, and for handloaders who are pushing the limits.
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Old 03-01-2009, 10:23 AM
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BOO!

I believe that the differences are more of the mythology and urban legend variety than anything else. I shoot them interchangeably in both ARs and bolt guns, have never had any hint of a problem.
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Old 03-01-2009, 10:49 AM
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Per ATK (owns Federal, Speer etc) the "XM" acromyn indictes ammunition that is military contract over run ammunition that may or may not meet all relevent military contract specifications.

epj- do not generalize from the specific instructions of a given manufacturer. Your manual states that a recent production Mini-14 is safe to use either type of ammo. That indicates only that the chamber in recent Minis will allow the usage.
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223, 357 magnum, chamber pressure, commercial, hornady, military, remington, ruger, winchester

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