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Thread: 5.56mm NATO versus 223 Remington Chamber Differences

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    5.56mm NATO versus 223 Remington Chamber Differences

    5.56mm NATO versus 223 Remington Chamber Differences

    A SAAMI spec .223 Remington chamber will have a shorter leade with a sharper angle to the leade and a shorter amount of effective freebore than a 5.56mm NATO chamber. The freebore itself will also be narrower in the .223 Remington chamber.




    raw pics courtesy of Ned Christiansen



    With all other things being equal, the 5.56mm NATO chamber with its longer and shallower angled leade and longer amount of effective freebore will produce less chamber pressure than a .223 Remington chamber, when firing .223 Remington SAAMI Spec ammunition. Because of this, 5.56mm NATO amunition can be loaded to a pressure that would be considered excessive in a .223 Remington chamber, yet acceptable in a 5.56mm NATO chamber. (Pressures are measured using different methods between the two systems.)


    The leade of a SAAMI 223 Remington chamber.







    The official SAAMI 223 Remington drawing.




    From Jeff Hoffman, co-owner of Black Hills Ammunition

    “The 5.56 IS a higher pressure/velocity cartridge, but it is made to a military standard, with different test methods, (and therefore is not easily directly comparable to .223 pressures) . . . the general spec for US 5.56 ammo is 58,700 psi max, measured at case mouth. . . Please note this is a different method than SAAMI transducer or copper crusher, as used on commercial ammunition. 5.56 ammunition spec results in ammunition loaded to a higher pressure level than commercial .223, but the test methods specified are different . . .The spec calls for a different pressure test method than SAAMI spec ammo, and is not directly comparable . . . “



    Here's a very interesting quote posted by Ned Christiansen on M4carbine.net:


    ". . . In short, you can safely fire all 5.56 AND 223 ammunition in a gun properly chambered for 5.56. You MUST NOT fire 5.56 ammunition in a 223 rifle. As case in point, I fired XM193 5.56 ammunition in a 223 test barrel with average pressures (conformal transducer) of 72,550 psi, and peak pressure registered at 76,250 psi. . ."

    Since the SAAMI MAP for the .223 Remington is 55,000 PSI, that puts XM193 fired from a minimum spec .223 Remington chamber at 17,550 PSI over the maximum.





    (The following is just a generalization to demonstrate the concept. DO NOT hold me to the exact numbers as they are not correct and they ignore the difference due to the different methods used to measure chamber pressure.)

    Consider the left graph pictured below; M193 fired in a 5.56mm chamber. The pressure is within the MAP limit. Now, take the exact same round, (same powder, same charge of powder) and fire it from a .223 Remington chamber; pictured in the right graph below.

    Because the .223 Remington chamber has a shorter and sharper angled leade compared to the 5.56mm chamber as well as a shorter effective free-bore, the bullet engages the rifling sooner in the .223 chamber than it would have in a 5.56mm chamber. This causes the pressure to rise faster, peak sooner and reach a higher (and per SAAMI, unsafe) level than it would have if the round had been fired from a 5.56mm chamber.






    Many people seem to incorrectly believe that 5.56mm brass cases have significantly reduced case capacity compared to .223 Remington cases. The table of case capacities shown below demonstrates that this notion is false.









    .....
    Last edited by Molon; 11-28-15 at 11:29.

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    Molon, thank you for posting this - objective and concise.

    Can I nominate this one for sticky status?
    Ken in Illinois

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    Finally. Is there a pressure trace diagram to go with the measurement claims? The above charts look like QuickLoad.
    Last edited by acrashb; 06-15-10 at 20:11.

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    great stuff
    "Intelligence is not the ability to regurgitate information. It is the ability to make sound decisions on a consistent basis "--me

    "Just remember, when you are talking to the average person, you are talking to a television set"--RDJB

    One Big Ass Mistake America

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    Very informative. Thank you.

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    The next most popular chamber seems to be the .223 Wylde. Do you have any good information regarding the .223 Wylde chamber dimensions? I read a post somewhere that was supposedly by Bill Wylde that he used 5.56 dimensions and only added additional free bore for the longer 80gr bullets. I have also read elsewhere that the body of the Wylde chamber is tighter than 5.56. I would love to know the real scoop about this chamber.

    Thanks and great post!

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    well put!

    Quote Originally Posted by M&P45 View Post
    The next most popular chamber seems to be the .223 Wylde. Do you have any good information regarding the .223 Wylde chamber dimensions? I read a post somewhere that was supposedly by Bill Wylde that he used 5.56 dimensions and only added additional free bore for the longer 80gr bullets. I have also read elsewhere that the body of the Wylde chamber is tighter than 5.56. I would love to know the real scoop about this chamber.

    Thanks and great post!
    just don't mix it up in the wrong way -the old adage ,your face is ugly but its the only face you have ! don't push your luck !! for ar's 5.56 chamber is very good ,why play games with what works ! a few years ago, i seen a dpms m-4 style blow primers on m885 lake city ammo but shooting rem.223 no primer blown.. yes you guess it had .223 chamber also add in some ill chromed barrels as well ...new barrel time !!!
    Last edited by cz7; 09-09-10 at 20:38. Reason: opps

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    Quote Originally Posted by cz7 View Post
    just don't mix it up in the wrong way -the old adage ,your face is ugly but its the only face you have ! don't push your luck !! for ar's 5.56 chamber is very good ,why play games with what works ! a few years ago, i seen a dpms m-4 style blow primers on m885 lake city ammo but shooting rem.223 no primer blown.. yes you guess it had .223 chamber also add in some ill chromed barrels as well ...new barrel time !!!


    Umm WTF are you saying?


    .223 Wylde is not the same as .223 Rem.


    There have been at least a couple chamberings that are meant to bridge the gap between 223 and 556. You get to shoot 556 in a Wydle chamber with better accuracy than a 556 chamber. I believe the Noveske chambering is very similar. To me the Wylde and Noveske chamberings offer the best of both worlds because of the ability to shoot either round while maintaining 223 accuracy. 556 is fine for a combat gun but not ideal for a precision rig.

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    Quote Originally Posted by M&P45 View Post
    The next most popular chamber seems to be the .223 Wylde. Do you have any good information regarding the .223 Wylde chamber dimensions? I read a post somewhere that was supposedly by Bill Wylde that he used 5.56 dimensions and only added additional free bore for the longer 80gr bullets. I have also read elsewhere that the body of the Wylde chamber is tighter than 5.56. I would love to know the real scoop about this chamber.

    Thanks and great post!
    The Wylde chamber has a longer leade/freebore dimension, the same leade angle and a tighter neck than a NATO chamber. From ar15barrels.com:

    http://www.ar15barrels.com/data/223-556.pdf
    Last edited by jmart; 09-09-10 at 20:58.

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    Thanks Molon, I have decided to stock up on ammo and a few mags while I am saving up for my M4 and I picked up some .223 on the recomendation of the salesman...I wasn't sure if I could use it in a rifle chambered for 5.56 (I know newb move) but I'm at ease now

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