Ammo .556

Discussion in 'Large-Bore/Small-Bore Rifle/Shotgun' started by Theorich, Mar 14, 2017.

  1. jim brady

    jim brady Well-Known Member

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    Don, there was a time in the early development of the 5.56mm when the rifling twist rate was found to 'understabilize' the bullet, and supposedly, the round was reported to cause horrible wound channels from early battlefield reports.

    When the 5.56mm was "improved" for greater accuracy, and the twist rates changed to properly stabilize the bullet, the "lethality" was diminished. If you get the time, look up the "Ichord Hearing Report" as reported in the Atlanta Monthly Journal. It really is a fantastic read. The report is an easy read, and covers exactly what you mention, as well as the Army Ordinance Department's role in making major changes to the early (and disastrous) propellants and M16 rifle design.
     
    Don Fischer and SilasW like this.
  2. jwdurf

    jwdurf Well-Known Member Supporting Member

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    The difference is that the 5.56 is a different round than the .223. The chambers are slightly different and the cartridges are loaded to different pressures.
    http://www.mlefiaa.org/files/ERPR/223_vs_556.pdf
     

  3. Don Fischer

    Don Fischer Well-Known Member

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    I just looked in the Hornady manual and looked at demintion's of both. In that manual there exactly the same!
     
  4. jwdurf

    jwdurf Well-Known Member Supporting Member

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    You're disagreeing with SAAMI and Federal, not with me. I'm done.
     
  5. Pawpaw40

    Pawpaw40 Well-Known Member

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    The ammunition dimensions are basically the same. I believe they use a different datum point to determine the shoulder. The chamber dimensions are not the same. 5.56 has quite a bit more freebore than the 223, and so can cause chamber pressures to increase.
    Here is a link to reamer dimensions for 223 and 5.56 chambers, provided by the makers of the reamers.
    http://ar15barrels.com/data/223-556.pdf

    From what I have read, Weatherby magnums have a large amount of freebore also. Trying to load too close to the rifling can cause high pressures there also.
     
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