LOW PRESSURE .223 ROUND FOR AR PISTOLS?

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  • marte616

    God bless America...
    MDS Supporter
    Apr 15, 2008
    1,355
    Occupied Territory
    Fellas,

    I was wondering...is there a commercially available .223/5.56 round designed to produce lower chamber pressures (50K PSI, I read somewhere here IIRC) created when you fire a 55g FMJ through a 7" pistol build?

    Additionally, I have read that a 55-62gr bullet fired from any barrel shorter than 11 or so inches will go through soft tissue without tumbling, therefore not disabling an adversary as promptly as needed. Wouldn't firing a round with lower amount of power, reducing terminal speed (subsonic even?) enhance the terminal ballistics of the bullet, again, when fired from a very short barrel?

    I worry about barrel and upper internals' longevity. But foremost, I worry about my face being blown off by excessive pressure causing stress on the upper and it blowing up.

    If not, why? Is it not feasible? If it is, has anyone tried it? Lastly, if it hasn't been done and it can be done, it sounds like a great business idea, given the increasing popularity of the AR pistols.

    I would like to hear your analysis.
     

    ironpony

    Member
    MDS Supporter
    Jun 8, 2013
    7,189
    Davidsonville
    My first thought is the 300 blk round, if one is buying another barrel (short 223) why not .300. Lower velocity but ~ 4 times the weight in a round - 220 gr. Much lower pressures, even a 110 gr. Pill can be kept under 50k cup and reach 2,000 fps .
    I not sure if this helps your thought pattern but thought I would mention it.
     

    BigT5g

    Ultimate Member
    May 12, 2014
    1,442
    Dayton MD
    I would NOT rely on the effectiveness any 5.56/.223 round traveling under 2600-2700fps whether the reduction of velocity is because of a anemic load or short barrel. The stopping power of this round has a lot to do with fragmentation, and velocities below the above threshold won't fragment reliably.
     

    Pinecone

    Ultimate Member
    MDS Supporter
    Feb 4, 2013
    28,175
    No, the problem is, out of a short barrel the velocity is LOWER, and this is why they do not have as good of terminal ballistics.

    So you need MORE pressure and MORE velocity.

    Or shoot heavier bullets that are more marginal on stability.
     

    Magnumite

    Ultimate Member
    Dec 17, 2007
    6,561
    Harford County, Maryland
    Part of the effectiveness of the 223/5.56 round comes from the yaw angle the bullet impacts. This was found to be a short coming of the SS109/M855 rounds, effecting fragmentation. The new 'green' round is actually much better....but not available. Plus it is not a reduced load.
     

    erwos

    The Hebrew Hammer
    MDS Supporter
    Mar 25, 2009
    13,866
    Rockville, MD
    I would NOT rely on the effectiveness any 5.56/.223 round traveling under 2600-2700fps
    This is only really true of M193/M855/SS109. The higher end stuff does better at lower velocities... to quote the ARFCOM Ammo Oracle for some potential choices:
    68 grain Hornady Match OTM
    69 grain SMK OTM
    75 grain Hornady TAP
    77 grain Nosler OTM

    Of course, ~7.5" AR pistols are toys anyways. If you need a gun to save your life, grab a 16" barreled rifle. :)
     

    clandestine

    AR-15 Savant
    Oct 13, 2008
    37,031
    Elkton, MD
    No.

    I can say with almost certainty that, if a company was able to pull it off, it would be a huge mess. People would buy it and try it in their regular AR and have issues and then complain.

    Why you say? Because there is a LOT of stupid people in the world.

    If you are having overpressure signs on your AR pistol have the throat cut to true 5.56 specs (Reduces pressure), use a M16 carrier (Adds mass which slows unlocking), put adjustable gas (SLR works best), H Buffer (Adds Mass but not too much), and a Chrome Silicone Flat Wire Action Spring (Adds more resting load).
     

    Pinecone

    Ultimate Member
    MDS Supporter
    Feb 4, 2013
    28,175
    This is only really true of M193/M855/SS109. The higher end stuff does better at lower velocities... to quote the ARFCOM Ammo Oracle for some potential choices:


    Of course, ~7.5" AR pistols are toys anyways. If you need a gun to save your life, grab a 16" barreled rifle. :)

    The M262 load of the 77 grain OTM is 2750 fps muzzle velocity.

    And it exhibits significant yaw in soft targets.
     

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