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**Difference of .223 & 5.56 ?

ns916ns916 Member Posts: 31 ✭✭
edited February 2005 in Ask the Experts
I was looking into buying an AR-15 upper from an online store and in the "Choose Chamber" drop down box for options, it has a choice of .223 REM or 5.56 NATO. I was under the impression these calibers were completely interchangable. Is this incorrect? I thought you could shoot either/or out of AR's so why the choice in chamber? Will this obligate me to shooting 1 and not the other?
Thanks in advance.

"The name's Oxbig, Mike Oxbig"


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    ghalleenghalleen Member Posts: 11 ✭✭
    edited November -1
    I read just last month in one of my gun magazines that the 5.56mm is loaded to higher pressures and has thicker cases. According to the article, you can fire .223 in a 5.56 rifle, but shouldn't shoot 5.56 in a .223.

    Unless the manufacturer says otherwise...
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    nononsensenononsense Member Posts: 10,928 ✭✭✭✭
    edited November -1

    Here are a couple of bits that can give you a little more insight into these chamberings.

    .223 SAAMI Spec Vs. 5.56 Nato

    If we are talking about .223 Remington SAAMI-spec chambers in an AR15, OH NO!
    Do NOT use such a chambering if you EVER plan on shooting any military NATO 5.56 ammo, which happens to be only the most common, least expensive and most widely used AR15 cartridge available in all the world. In other words, NEVER buy/use a SAAMI-spec chamber in a battle rifle, especially if the barrel and chamber are chromed, as you cannot fix it!
    Here's the problem. Many NATO cartridges have bullets that will become jammed into the rifling of a SAAMI chambering (the throat is too short). This is VERY DANGEROUS, for a great number of reasons.
    Fulton Armory uses a "5.56 Match" chambering in its rifles/uppers/barrels (in fact our barrels are marked as such), which is a slightly modified SAAMI chamber with a tad longer throat to accommodate NATO bullets. The Fulton Armory 5.56 Match chamber allows for the safe and reliable use of all SAAMI and NATO ammo, while offering the accuracy potential of the SAAMI chambering with match commercial cartridges. Remember, there's often a large difference between bolt guns and military rifles. This particularly true for the 5.56 vs. .223; Fulton Armory is well known for the finest performance for any given platform, and our 5.56 Match chamber is one way we achieve that performance with the AR-15-type rifle.
    Hope this helps.
    Best regards,
    Clint McKee


    We are often asked whether our rifles feature NATO (North Atlantic Treaty Organization) or SAAMI (Small Arms and Ammunition Manufacturers Institute) standard chambers, and whether it makes any difference.


    .223 Remington (SAAMI standard) and 5.56mm (NATO standard) rifle chambers are almost identical. The difference is largely limited to the "freebore," the cylindrical space in front of the case mouth, and the "lead" or "leade," the the tapered region that eases the bullet into full engagement with the rifling. NATO and SAAMI cartridges can normally be used interchangeably with no problem.
    The SAAMI chamber features less freebore and a tighter leade, which normally provide better bullet fit and match-grade accuracy than the NATO chamber. It is wonderfully suited to match bullets.
    Millions of rounds of NATO ammunition have been fired safely in Eagle Arms' and ArmaLite's SAAMI chambers over the past 15 years. Occasionally a non-standard round (of generally imported) ammunition will fit too tightly in the leade, and resistance to early bullet movement can cause elevated chamber pressures. These pressures are revealed by overly flattened or powder stains that reveal gasses leaking around the primer.
    The first few rounds of ALL ammunition, from whatever source or lot, should be checked for pressure and other signs of defect before firing large quantities. If you have a problem, you can generally bet that the ammunition meets neither SAAMI nor NATO specifications.
    ArmaLite has adopted a practice of using a special, modified SAAMI chambers in its stainless steel match barrels. This chamber is better for match use than the NATO chamber, but fires the NATO ammunition perfectly. We use the NATO chamber in all moly (phosphated) and chrome-lined barrels.
    ArmaLite's larger AR-10r rifles are all chambered with 7.62mm NATO chambers. .308 Winchester (SAAMI standard) ammunition functions perfectly in the 7.62mm chambers.

    c 2001 ArmaLite, Incr.
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    D@DD@D Member Posts: 4,407
    edited November -1
    If you do a search you will find many many threads on this topic.
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