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Thread: The difference between the .223 Remington and 5.56x45 mm

  1. #1
    Distinguished Member T.S.'s Avatar
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    The difference between the .223 Remington and 5.56x45 mm

    For those of you who are new to the AR-15 and have asked the question ....

    .223 Remington Vs. 5.56: What's in a Name?

    There is much confusion between the .223 Rem. and the 5.56 NATO rounds.

    http://www.americanrifleman.org/arti...ats-in-a-name/
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    Sponsor brownie's Avatar
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    When shooting 556 through a 223 chamber, check the first two rounds for signs of over pressure. None found, shoot away, the chamber is not too short and will handle it.

    Far too many ar's chambers are cut to accept both dimentionally [ like the M1a's are chambered to accept either the 762x51 or 308 ] to discount 556 out of 223 chambers without checking for over pressures to determine a particular 223 ar shouldn't be running 556.
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    Distinguished Member GD2A's Avatar
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    Quote Originally Posted by brownie View Post
    When shooting 556 through a 223 chamber, check the first two rounds for signs of over pressure. None found, shoot away, the chamber is not too short and will handle it.

    Far too many ar's chambers are cut to accept both dimentionally [ like the M1a's are chambered to accept either the 762x51 or 308 ] to discount 556 out of 223 chambers without checking for over pressures to determine a particular 223 ar shouldn't be running 556.
    I'm just learning about these matters myself - why can the M1A do it and some AR's cannot?
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    Sponsor brownie's Avatar
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    Quote Originally Posted by GD2A View Post
    I'm just learning about these matters myself - why can the M1A do it and some AR's cannot?
    Some ar's are chambered for only 556 or only 223. The M1a always had their chambers cut to accept both.
    The mind is the limiting factor

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  5. #5
    Senior Member DGOrlando's Avatar
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    Quote Originally Posted by brownie View Post
    Some ar's are chambered for only 556 or only 223. The M1a always had their chambers cut to accept both.
    You can safely shoot .223 in AR's chambered for 5.56 only; but not the other way around. You'll be giving up some accuracy though.

  6. #6
    Sponsor brownie's Avatar
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    Correct, just be aware that many 223 ar's chambers are cut for both to be used, hence you have to determine if there's signs of over pressure in your first couple of rounds of 556 through one. No signs of over pressure and you've got an ar that will handle both.

    One thing to remember as well is that the 556 throat being longer, as erosion occurs the 223 could cause problems at that time. Usually around the 5K mark of rds through the barrel.
    The mind is the limiting factor

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    Distinguished Member 10x's Avatar
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    Great tips Brownie

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    Senior Member Beacher's Avatar
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    How would one identify "signs of over pressure" Brownie?
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    Sponsor brownie's Avatar
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    Check the casing primer. Over pressure will show the primer flattened. Also check the case overall for any bulging, particularly around the base.
    The mind is the limiting factor

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    Brownie

  10. #10
    Senior Member Beacher's Avatar
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    Irregular bulging of the wall I knew was a sign of trouble, but thank you for the clarification. I was concerned when you said evidence of over pressure you might have been referring to something you would see occurring to the upper, maybe in the chamber area. But a flat primer I have not heard about. Tried to find a picture showing normal post shot primer and one showing "flat" but was unsuccessful. Anyone have pics of the two for clarification? Save us 1,000+ words?
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