I don't post much, but everyone here have always been very helpful when I have a dumb question to ask. I recently read an article about Rock River Arms Tactical CAR A4, it says chambered for 5.56 NATO which is important if owner intends to use surplus mil-spec ammo in addition to 223 Remington. I guess my dumb question of the day is what is the difference? I always thought they were the same thing. Also, I've wanted an AR for a while and with the changes in govt. maybe should act while I still can. Anyone have any advice on lower priced weapons like those from Olympic or Bushmaster or others?
Thanks James

Hey Fuz, The 5.56x45 and the .223 are identical in size, but the Military round is hotter, it runs at a much higher pressure than the .223. Cases are thicker. I you are looking for an AR make sure you buy a 5.56 chambered. I have owned my Bushmaster DCM for about 9 years, put lots of rounds through her and not one part of it shows any wear. It is very accurate, and will give any bolt gun a run for it's money. Chrome lined bore and chamber, uses standard M16 or custom mags, no recoil to speak of. Good Luck, JP

Actually, not quite identical in size. The chamber dimensions for the NATO round are slightly longer, with minimum being about 4 mils greater than the SAMMI chamber minimum. The leade to the rifling is also a little further forward, and some NATO long bullets can jam into a .223 SAMMI chamber? The rated pressure for the NATO round is actually 10% lower than commercial .223 load maximums (52,000 PSI for NATO pressure, 55,000 PSI for SAMMI max pressure spec). However, when you shoot NATO rounds you often find they are hotter because the military gets them loaded to their actual number, while commercial loaders are timid and often load .223 down in the 40-45,000 PSI range. The NATO round's proof pressure, 70,000 PSI, is higher than the SAMMI maximum, and that confuses some people on the pressure issue.

Bottom line, you can fire .223 in a NATO chamber since the SAMMI maximum pressure is well below the NATO proof pressure, The SAMMI and NATO chamber length ranges overlap. In a long NATO chamber, the .223 will experience more case stretching than in a SAMMI chamber. You cannot reliably fire a NATO round in a SAMMI chamber because of the bullet jam problem. The heavier NATO brass has less internal capacity, which means .223 powder charges cannot be put in it, but must be worked up separately.

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Informative post Unclenick, but I think your typewriter made a mistake! The 5.56 is Not over 1/8 inch longer than a .223. Your post says 4 mils. which is about .160. How can that be? You hit the wrong key or left out the decimal point or something.

Otherwise, thanks for the info.

JB

Your post says 4 mils. which is about .160. How can that be?

The word mil comes from the Latin for 1000, as in millennium (a thousand years). Mil by itself is normally use to mean 1/1000, or thou. It has all kinds of definitions related to area and angle, and also of length. In the case of the metric system it would an alternative abbreviation to mm for millimeter, which is how you are using it. But in the inch measuring system, as it is used by tool makers and machinists in this country, it means 1/1000 of an inch, or 0.001". That is how I was using it here.

I lived through metric conversion in Canada and the chances of mix-ups are countless. As we have an international membership, it's best if we use something more specific than mils. 1.0 mm or .001" is specific.

Bye
Jack

The phrase "mil" as .001 of an inch must be peculiar to certain industries or areas. I worked as a toolmaker many years and never heard it used. This was a Connecticut based company, Pratt & Whitney, so we had folks from up north and all over the south working there.

The yankees did introduce us to the unit of "50 millionths", always spoken in a loud voice with the chest poked out, usually as a prelude to a story about how "we did it up north".

We always refered to .00005 as a "half a tenth".

I agree with the above... 5.56 has a higher chamber pressure due to a lower internal volume, caused by a thicker case wall thickness..... lower volume + same amount of propellent = Higher pressure... As to the FIX>>>> Buy a RRA that is chambered in .223Wylde. It has the best qualities of both chambers and will feed and fire anything... British s109 surplus to top o'the line Black Hills or Hornady..... ALSO if you opt for the 1:14 twist you will be limiting yourself on the ammo that you can use. 1:14 WILL NOT STABLIZE bullets above about 55 gr.... its not the weight really, its theoverall lenght and shape of the longer bullets that NEEDS the extra twist, but the 1:8 doesn't adversly affect the lighter stuff... Mine shots well below MOA out to 200yd with 62gr S109 surplus or 50gr Accumax, both are cheap so way spend the extra dough... Wolf ammo just sucks stay away..... Ed

If your shooting one of the NEF handi-rifles stay away from the military rounds. Sticking cases in them is a big problem.

The guys at AR15.com have a site called the Ammo Oracle that has a lot of good info you should take a look at. Some of the links may be a little dated, but there's way too much stuff to try to restate here. Go to http://www.ammo-oracle.com/body.htm

As far as choosing an AR, there are a lot of good choices out there. I have two Colt Match Targets, and two Bushmaster XM15's. In terms of overall quality, fit and finish, etc., there really isn't too much difference between them. IMO. A couple of friends of mine have Rock Rivers, and they are very good overall. In fact, I'd say the RR's I've tried have a little better triggers, out of the box, than many of the others. I think if you go with one of the major brands, like Armalite, Bushmaster, Colt, DPMS, Rock River, etc., you won't go wrong.

As usual, you guys are very helpful. Still researching my next purchase. AR.15 website looks helpful. thanks again,James

We are talking AR's? I can pull 100 rounds of M855(SS109)and 100 rounds of "you name the brand" .223. The differences are miniscule. Both will cycle in the others chamber. So the big difference is Pressure! An AR15 is not a bolt action, so the Jamming issue is Mute. Pressure, Pressure, Pressure!!!

As far as Arf.com goes, only believe less than 1/2 of what is posted.

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So there is a difference although it is rather small. Thanks folks, I learn something new every day.

Thanks again,

Jim

yes... thanks for an enlightening thread!!