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AR Build - What Barrel Length For M855

Discussion in 'Rifle Country' started by Code3GT, Oct 4, 2008.

  1. Code3GT

    Code3GT Member

    Jun 30, 2008
    Austin, Tx
    Planning out my AR build. Going to go with a stripped lower and complete upper as this will be my first build. I was looking at ammo prices and it seems M855 is cheaper than M193. 16" barrel enough to get the 855 downrange effectively? Sorry if this is a dumb question, again, new to building, only used to what the air force gave me :)
  2. taliv

    taliv Moderator

    Oct 23, 2004
    m855 is not normally cheaper than m193. where'd you find it?
  3. Hoppy590

    Hoppy590 Senior Member

    May 25, 2006
    MA :(
    M855 is about 10-20% more expensive per case as far as iv seen
  4. Float Pilot

    Float Pilot Senior Member

    Jul 27, 2007
    Kachemak Bay Alaska
    Some of us do tend to stumble into more M855 than the older stuff. His location and military history status will give you a hint why.

    While doing some active duty time, I compared M-193 to M855 from a :

    20 inch barreled M16A2 (1 in 7 twist) issue rifle using two chronographs at 20 ft.

    M-193 Ball = 3,140 fps Chrony
    3,126 fps Ohler 33

    M-855 ball + = 3,080 fps Chrony
    3,050 Ohler 33

    14.5 inch M-4 carbine (Issue) 1 in 7 twist

    M-193 Ball = 3,055 fps average between 2 chronographs

    M-855 ball+ = 2,852 fps average

    11.5 inch Bushmaster (my old patrol car trunk gun) 1 in 9 twist.

    M-193 ball = 2,710 fps Chrony

    M-855 Ball+ = 2,600 fps average

    Since 2,700 is considered the minimal impact velocity for a producing a serious wound channel, The 11.5 inch barrel does not cut the mustard unless you are within a few feet of your target.

    The 14.5 inch M-4 barrels also leave much to be desired for terminal effect after 100 meters.
  5. Dienekes

    Dienekes Senior Member

    Dec 26, 2002
    As far as effective fragmentation goes, I figure my M4gery (16" barrel) is about a 120 yard weapon with the M193 round or my handloaded 55 gr FMJBT equivalent. With military M855 that drops to about 90 yards--and I have trouble getting full velocity in my M855 type handloads, using the same bullet, with AA2520 which is the powder I use.

    Upshot is that I use the slightly reduced velocity of my M855 type load for practice only out to 100 yard as it prints closely enough to M193; but I would avoid it for serious social work.

    There is absolutely no doubt that anytime you shorten the 5.56 barrel under 20" you are giving up a lot in stopping power. So it depends on what you have in mind.

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