Ideal AR Pistol Barrel Length?

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  • calicojack

    American Sporting Rifle
    MDS Supporter
    May 29, 2018
    5,348
    Cuba on the Chesapeake
    Pondering a pistol build. Opinions on the ideal AR pistol barrel length? This will not initially be a suppressor host but might be in the future.
     

    sxs

    Senior Member
    MDS Supporter
    Nov 20, 2009
    3,377
    Anne Arundel County, MD
    5.56 has excessive muzzle blast and, at least the 2 I shot, only OK accurracy. The 5.56 with the worst blast was just 8 or 8.5 inches and it was hard to hold a group tighter than around 3 to 4 inches at 50 yds...which, to me sucks. I have a 9mm build (10 1/2 barrel) that shoots well with fairly minimal muzzle blast as it is a pistol cartridge shot from a fairly long, for a pistol, barrel. 300 Blackout also seems to produce somewhat less muzzle blast, in my very limited experience, in a pistol length. But I also never shot the 5.56 with a 10.5 in barrel at the same time as the 300 blackout....and I think the 300 may have been 11 or 11.5. Or it may have been my imagination since I was expecting a significant muzzle blast. Of course, it does make a difference in accuracy if you use a good grade or even match grade barrel no matter what length barrel you use. If you use a can, obviously muzzle blast is much less a factor. Then, of course, what does ideal mean for you? Handling, accuracy?
     

    Ammo Jon

    Ultimate Member
    Mar 3, 2008
    20,784
    A fellow forum member is helping me with mine, based on his recommendation I’m doing 10.5”
     

    Boats

    Beer, Bikes n Boomsticks
    Mar 13, 2012
    4,073
    Howeird County
    10.5 still has a fair amount of muzzle blast. What you gain is reliability, even moreso with an adjustable gas block.

    As far as accuracy is concerned, ammo and barrel mfr and twist matter.
     

    sxs

    Senior Member
    MDS Supporter
    Nov 20, 2009
    3,377
    Anne Arundel County, MD
    10.5 still has a fair amount of muzzle blast. What you gain is reliability, even moreso with an adjustable gas block.

    As far as accuracy is concerned, ammo and barrel mfr and twist matter.

    Yup. 5.56 was designed as a rifle round and needs more than 10 inches to burn the powder. I suppose a reloader could develop some loads with a somewhat faster powder to mitigate the blast in a pistol build. Also, heavier bullets may help somewhat but I've only shot factory ammo in my ARs and factory 55 gr in the 5.56 builds my friends had.
     

    Gcs7th

    Ultimate Member
    Jan 26, 2012
    1,280
    AGC
    Ideal for what barrel? Here’s my opinion

    22lr - 4”
    300blk - 8.5+”
    223 10.5”
    7.62x39 10.5”
    9mm - 5”
     

    DutchV

    Ultimate Member
    Jul 8, 2012
    4,703
    The Colt Commando was 10.3". 10.5" seems to be the minimum useful length for 5.56. Much shorter than that is going to make big fireballs.
     

    babalou

    Ultimate Member
    MDS Supporter
    Aug 12, 2013
    16,017
    Glenelg
    Pretty close to what Clandestine says

    Ideal for what barrel? Here’s my opinion

    22lr - 4”
    300blk - 8.5+”
    223 10.5”
    7.62x39 10.5”
    9mm - 5”

    Pretty dead on for the .223/5.56. Maybe even a little longer up to 11.5”-12.5”

    My .300 pistol is 8.5”

    Looking at the 7.62x39 recommendation you have... since 300 is 7.62x35 to me does the small difference make you choose 10.5? I would think 8.5-9.5”. I am not familiar with 7.62x39 pistols. I am sure Sir Chad will hopefully chime in
     

    04RWon

    Ultimate Member
    Feb 13, 2010
    5,178
    Orlando, FL
    I have a 10.5 noveske and an 11.5 bcm. Both have a2, m16 bcg, stt2 buffers, and spikes springs. The 11.5 has significantly less recoil impulse. It is much smoother.

    Ive watched velocity tests and it seems that extra inch does help out a decent amount in that aspect.

    Moving them around you cant tell the extra inch is there. That is not a fair test as the 11 is a lightweight build and the 10 is a standard profile and rail.

    Another consideration is what type of grip you want to run. Depending how you read the atf letter the tip of the barrel(not counting fh) to the end of the buffer tube, an 11.5 meets the 26” oal to allow a vertical grip. The letter says with stock fully extended(its a pistol so its not a stock?) but nowadays we have the beautiful sba3 which does extend so in that regard both exceed 26”.
     

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    04RWon

    Ultimate Member
    Feb 13, 2010
    5,178
    Orlando, FL
    Yup. 5.56 was designed as a rifle round and needs more than 10 inches to burn the powder. I suppose a reloader could develop some loads with a somewhat faster powder to mitigate the blast in a pistol build. Also, heavier bullets may help somewhat but I've only shot factory ammo in my ARs and factory 55 gr in the 5.56 builds my friends had.

    This^ from what I see anything below 10.3” isnt really good for reliability of the round or firearm.

    I was actually thinking 11.5 or 12.5

    Which barrel manufacturer were you considering?
     

    alucard0822

    For great Justice
    Oct 29, 2007
    17,643
    PA
    5.56 gets progressively more rude, as the barrel gets shorter, around 10.5" with carbine gas is about as short as practical. This is EXACTLY why 300BO has become popular, my 9" 300BO with full power supersonic ammo has about the same blast as a 16" in 5.56, but a more mellow tone, the gas pressures are lower with a longer dwell, so it tends to be easier to run reliably down to 8" or so, and of course is great suppressed, you can always swap to 5.56 with just a barrel, or build a 2nd 5.56 upper at a longer, more appropriate length (11.5"w carbine gas is nice).

    IMO if you want to build a fun pistol, strongly consider 9mm. The shorter the barrel, the quicker the dwell time, and the better the case seals before it starts to cycle, so less gas in the face, and good reliability if built properly. No gas system, and can go down to 4 or 5 inch barrels for a tiny AR(barrels are 1/2" shorter than an equivalent length rifle cal). You can shoot at steel and at most pistol ranges, still can reach out past 100yds, light recoil and blast, suppresses well, and cheap ammo. Much of the same can be said about a 22LR build too, but obviously then you miss out on most falling steel matches/ranges, and potential use as a SD/HD.

    These 2 are my favorite pistol builds, 9" 300BO on Aero M4E1 and 7" 9mm on a QC10, although I shoot the 9mm a LOT more, built it with a 3lug adapter for whenever my 9mm can gets out of NFA jail.
    20190419_093147.jpg
     

    GuitarmanNick

    Ultimate Member
    Jan 9, 2017
    2,221
    Laurel
    My 5.56 pistol is 10.5", is quite accurate to about 100 yards and can hit a target @ 200 yards if necessary. The 10.5" makes it function reliably and is a good balance on accuracy and mobility IMO.

    My 9mm is also 10.5" and is for targets within 50 yards. This length gets the best accuracy for the 9mm by allowing it to develop the cartridge's maximum velocity before leaving the barrel. Shorter or longer barrels will be less accurate because they either do not take advantage of all of the powder charge when too short, or slow the projectile down from friction when too long.

    The 10.5" is pretty much point and shoot within 50 yards and it should be on target and have enough energy to be effective. Beyond that range, the loss of energy makes the 9mm much less effective with substantial drop from point of aim.

    If you are going to run it suppressed, then you may want to consider a very short barrel. Perhaps 4" or so to insure the round stays sub-sonic. This brings a host of reliability issues with it and should be thoroughly tested before betting you life on it.
     

    erwos

    The Hebrew Hammer
    MDS Supporter
    Mar 25, 2009
    13,866
    Rockville, MD
    I'd vote 11.5". Like twice the dwell time makes it far more reliable than a 10.5" without doing things that will negatively impact long-term reliability (like oversizing the gas port).
     

    Bountied

    Ultimate Member
    Apr 6, 2012
    6,893
    Pasadena
    I had a 5.56 with a 8.5" barrel. It was only good for making fireballs and being loud, past 75yds it was crap. I sold that upper to make a .300 build My .300BLK with 10.5" barrel and 220gr sub loads can hit a 12" plate at 200yds easily and consistently. I'm looking into build a 9mm pistol now, I just don't really like the direct blowback of most 9mm AR type rifles. Maybe a CMMG upper is in my future. Something with a delayed blowback.
     

    j_h_smith

    Ultimate Member
    Jul 28, 2007
    28,516
    Can you imagine the tuning it took to get that firearm consistent. That's not a blowback design. I don't see how they did it.
     

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