.223 vs. 5.56?

This is a discussion on .223 vs. 5.56? within the Defensive Ammunition & Ballistics forums, part of the Defensive Carry Discussions category; .223 vs. 5.56 rounds? Can anybody tell me what the difference is between the .223 round and the 5.56? I know that the 5.56 is ...

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Thread: .223 vs. 5.56?

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    Member Array BlackJack's Avatar
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    .223 vs. 5.56?

    .223 vs. 5.56 rounds?

    Can anybody tell me what the difference is between the .223 round and the 5.56?

    I know that the 5.56 is rated at a higher pressure and the chambers are different (the 5.56 chamber has a longer leade (I think it is called, but am not sure what it really is).

    My question has to do with the ammunition itself. Are the .223 and 5.56 dimensionally the same? Does the 5.56 have more powder or powder with a different burn rate? What is it that makes the 5.56 have higher pressure, and thus makes it unwise to use in a weapon chambered for .223 while you can use .223 in a weapon chambered for 5.56?

    I am curious because I am seeing four different things:

    1. What people say – use .223 in a 5.56 chambered weapon but NEVER the other way around.
    2. SAAMI rating.
    3. NATO EPVAT ratings (which is measured in a different location than SAAMI so I am not sure how the two correlate).
    4. CIP (which also defines the chamber specifications for .223 as being different than the 5.56, but defines the “maximum service and proof test pressure” of the .223 as being equal to the 5.56)


    The whole reason that this has come up for me is that I am having a rifle rebarrelled and the gunsmith said I would have to go with .223 in order to get the accuracy guarantee, but that it would not hurt it to run 5.56 thru it occasionally.

    So, if anybody can tell me what the difference is between the .223 and the 5.56 ammo itself, I would greatly appreciate it.

    Thanks.

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    Senior Member Array BamaSteve's Avatar
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    Do a quick I know there was a couple very informative threads on this not too long ago.
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    VIP Member Array Thanis's Avatar
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    I have read and have been told:

    It is safe to fire .223 Rem out of a 5.56 x45mm NATO.

    It is safe to fire .223 Rem out of a .223 Rem.

    It is safe to fire 5.56 x45mm NATO out of a 5.56 x45mm.

    It is not safe to fire 5.56 x45mm NATO out of a .223 Rem.

    There are also things like barrel twist to consider. Check out this link:

    http://www.defensivecarry.com/vbulle...remington.html

    From that thread, MattLarson noted the psi.

    Quote Originally Posted by MattLarson View Post
    .223 Remington maximum safe chamber pressure is ~ 50,000 psi.
    5.56 maximum safe chamber pressure is ~ 60,000 psi. In addition, shooting 5.56 in a .223 chamber may cause significant increases in pressure due to the difference in chamber dimensions. Do not shoot 5.56mm NATO-spec ammo in a .223 Remington chamber. There's a ton of good info on this on the net. Here's just one of the many articles out there: The Gun Zone -- SAAMI on 5.56 v. .223 Remington Matt
    Note: The opposite has been stated for 7.62x51mm NATO vs .308 Win. Safe to fire 7.62x51mm NATO out of a .308 Win. Not safe to fire a .308 Win. out of a 7.62x51mm NATO. A bit of an argument on how safe is safe, but this is a side issue from your OP.
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    VIP Member Array automatic slim's Avatar
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    You are correct.........

    Quote Originally Posted by BlackJack View Post
    .223 vs. 5.56 rounds?

    Can anybody tell me what the difference is between the .223 round and the 5.56?

    I know that the 5.56 is rated at a higher pressure and the chambers are different (the 5.56 chamber has a longer leade (I think it is called, but am not sure what it really is).

    My question has to do with the ammunition itself. Are the .223 and 5.56 dimensionally the same? Does the 5.56 have more powder or powder with a different burn rate? What is it that makes the 5.56 have higher pressure, and thus makes it unwise to use in a weapon chambered for .223 while you can use .223 in a weapon chambered for 5.56?

    I am curious because I am seeing four different things:

    1. What people say – use .223 in a 5.56 chambered weapon but NEVER the other way around.
    2. SAAMI rating.
    3. NATO EPVAT ratings (which is measured in a different location than SAAMI so I am not sure how the two correlate).
    4. CIP (which also defines the chamber specifications for .223 as being different than the 5.56, but defines the “maximum service and proof test pressure” of the .223 as being equal to the 5.56)


    The whole reason that this has come up for me is that I am having a rifle rebarrelled and the gunsmith said I would have to go with .223 in order to get the accuracy guarantee, but that it would not hurt it to run 5.56 thru it occasionally.

    So, if anybody can tell me what the difference is between the .223 and the 5.56 ammo itself, I would greatly appreciate it.

    Thanks.



    Dimensionally the .223 and 5.56mm are the same, in fact I use military surplus brass in my Colt AR-15. The 5.56 is loaded to higher pressures, that's the reason for the extra freebore (leade).
    You can use .223 in a 5.56 rifle, but it might not function the action due to the lower pressure. I tried 5.56 in my Colt and there were signs of excess pressure, i.e. flattened primers.
    Regarding accuracy, I remember when I was in the army, our M-16's were extremely accurate when fired semi-auto. I think accuracy is more a function of the gun and shooter.
    Now, if you plan to do any reloading, the manuals I've seen use 5.56 and .223 data interchangably. However when using the minimum load of AA 2230 I got high pressure signs with military brass (which is supposed to be thicker). Reduce the starting load by 10% if you plan to reload. One other interesting aspect, when I used to use Win. 748 I had to load about 1 grain over max, just to get the action to function. I'm not sure if Colt AR-15's are built to military spec or not.
    I guess the bottom line is to watch for signs of excess pressure if you go with a .223 barrel. Personally I would go with the 5.56, that way you could fire both without worry.
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    Distinguished Member Array Tally XD's Avatar
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    Isnt this already running here
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    eschew obfuscation

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    Member Array BlackJack's Avatar
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    Based on most of these responses, I don’t think I did a very good job asking my question. I have read the referenced post and did not see what I was looking for.

    What I am really after is this:

    The ammunition itself is made up of 4 components (I think, I am not a reloader myself):

    1. The case.
    2. The primer.
    3. The powder.
    4. The bullet.

    If these two rounds are different and the 5.56 does have higher pressure then there must be something about one, or more, of these components that is defferent between the two. I am trying to determine which one it is, and what that difference is.

    I probably should have kept anything about specs and chamberings out of the original post itself.


    Automatic Slim,
    If I understand you correctly, you are saying that the military brass has thicker walls, causing the internal dimensions of the case to be smaller and that, in and of itself, causes the higher pressure. Am I understanding you correctly?

    If so, then what about the commercial 5.56 ammo? Does it also use brass with thicker walls?

    Are there any other differences?

    Thanks again.

  9. #8
    Senior Member Array jem102's Avatar
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    Quote Originally Posted by BlackJack View Post
    Based on most of these responses, I don’t think I did a very good job asking my question. I have read the referenced post and did not see what I was looking for.

    What I am really after is this:

    The ammunition itself is made up of 4 components (I think, I am not a reloader myself):

    1. The case.
    2. The primer.
    3. The powder.
    4. The bullet.

    If these two rounds are different and the 5.56 does have higher pressure then there must be something about one, or more, of these components that is defferent between the two. I am trying to determine which one it is, and what that difference is.

    I probably should have kept anything about specs and chamberings out of the original post itself.


    Automatic Slim,
    If I understand you correctly, you are saying that the military brass has thicker walls, causing the internal dimensions of the case to be smaller and that, in and of itself, causes the higher pressure. Am I understanding you correctly?

    If so, then what about the commercial 5.56 ammo? Does it also use brass with thicker walls?

    Are there any other differences?

    Thanks again.
    "ALL" four of the cartridge components you list will and can have direct bearing on pressure. NATO rounds are loaded to a higher pressure BECAUSE the 5.56 NATO chambering allows for it with a longer free bore. The greater barrel volume created by this free bore allows for a round with higher pressure.

    This higher pressure can be obtained by changing the "combination" of any of the following:

    1. Thicker or thinner case walls (W-W and Mil. Spec. LC have the same water capacity) may or may not change pressure depending on powder charge or primer type.

    2. Primer, Mil. Spec. primers do have thicker and harder cups than some bench rest primers as well as a higher/longer ignition cycle and will take/generate more pressure. The load is developed accordingly.

    3. Powder charge weights (depending on "burn" rate) are developed to suit a specific purpose. In the case of NATO rounds it is to run through full and semi autos built for combat. Once the application is determined the load is developed to the "working" design limits of the firearm by the combination of "closed bomb" and "universal receiver" pressure gun tests to achieve that level.

    4. Bullet weight has the single largest effect on pressure. The heavier the bullet the quicker and higher the initial pressure rise. Again, once the bullet weight is determined for the task at hand (all kinds of considerations here but for anti-personnel rounds it is generally the max. kill distance required that indicates bullet weight. The greater the distance the heavier the bullet needs to be to the point of "diminishing return" which with the .223/5.56 is about 75-80 gr. out to 600 yd.) When the weight is determined they go to the "closed bomb" and "pressure gun" testing methods.

    I.E. Both my AR's will take XX.x grains of RL-15 powder with a 75 gr. Hornady bullet and Rem. 7.5 primers using LC cases. If I keep to the same bullet, LC case and powder but change to a W-W primer I MUST reduce the powder charge by .5 grains or the W-W primer will pierce/blow out because it has a lower pressure threshold than the Rem. 7.5.

    You can NOT ( this is a safety issue for you and those around you) treat the components as "mutually exclusive", ammo is a "package deal" with fixed terminal applications.
    The NATO round and the NATO chamber are a matched pair as are the .223 Rem. and its chamber and any derivatives there of: Wylde, CLE, Krieger, WOP etc.

    Get a loading book from Sierra, Hornady, Lyman, Speer or Nosler, They all have detailed explanations of the process as well as load data should you want to go that route.

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