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AR uppers...10.5" vs. 11.5"?

Discussion in 'General Firearms Forum' started by emt1581, Aug 20, 2012.

  1. emt1581

    emt1581 Curious Member

    19,885
    2
    Oct 17, 2002
    Penn's Woods
    I'm building a pistol. Recently I read that a 10.5" won't cycle reliably whereas an 11.5" will give the bcg 40% more energy to cycle with...or something along those lines.

    Anyone have experience with either length?

    Thanks

    -Emt1581
     
  2. collim1

    collim1 Shower Time!

    7,494
    1,026
    Mar 14, 2005
    USA
    Buddy at work has a dept issued 10.5" entry gun. It works and is reliable, but have never put it on a chrono.

    I imagine it is somewhere in the .22mag+P range.

    I know for a fact it is reliable with 55gr ball and 64gr Gold Dot HP. It makes serious flash and noise though, even with earplugs. I usually wear plugs and muffs when shooting it.
     


  3. I've owned both 10.3" and 10.5" uppers and both worked 100% reliably, although they both came as either a complete rifle or complete upper.
     
  4. KalashniKEV

    KalashniKEV

    6,391
    3
    Sep 24, 2003
    NoVA
    All 7" gas systems use the same tube, and for a long time, the same port.

    Even with the properly sized port, adding that extra inch increases the dwell time that the gas has to act on the bolt before the bullet exits the muzzle and it all dissipates.

    Back in the days of XM177s, CARs, and Commandos, the 10.5 A1 FH guns were not as reliable as the ones fitted with the 4.5" moderator. The Commando moved to an 11.5" barrel and solved this.

    Then people wanted ~10" guns again, and ran into similar problems. The Noveske KX3, a copy of the Bulgarian 4 piece fatty, solved this... and made the guns almost as long as the 11.5" guns.

    Then they got smart and started looking at port size, suppressed/ unsuppressed, and now there are more reliable short guns, switchblocks, etc...

    See the Mk18.
     
  5. WoodenPlank

    WoodenPlank Who?

    7,958
    3
    May 15, 2010
    NW Florida
    My go-to weapon is a Mk. 18 RIS II clone. LMT 10.5" upper, DD RIS II rail, BCM FA BCG and H2 buffer. I ditched the KX3 I had used previously because of weight.

    I just got done rebuilding it (replaced rail and BCG), and so far it has been 100% reliable with anything and everything I have fed it. Wolf (5.56 and .223), Tula, Silver Bear, Federal/LC XM193 all run perfectly with good ejection pattern.

    If I had to do it all over again, though, I probably would have gone with an 11.5" BCM upper with the same rail system, or possibly a factory Colt COmmando SBR.

    The KX3 was really intended for the 7" PSD type uppers, as I remember. While it can help on a 10.5" upper with a poorly sized gas port or a worn out BCG, it's not really needed in most cases. Plus, on the 10.5" and longer guns, that KX3 puts a lot of weight way too far foward.
     
  6. KalashniKEV

    KalashniKEV

    6,391
    3
    Sep 24, 2003
    NoVA
    [​IMG]

    That's true... I put the tilde in there because I didn't want the OP to say, "OMGosh... 7 inches???"

    FTR, AR pistols are stupid.
     
  7. Travclem

    Travclem Badass Member Lifetime Member

    6,775
    11
    Aug 4, 2008
    Lubbock, TX
    55gr ammo has shown to have about a 350fps drop from 16" to 10.5". Assuming the same is true of the heavier loads, my MK262 (2723fps, 16") clone should be around 2373fps from my 10.5". I'll put it on the chrono when my tax stamp comes back. I would imagine it to be quite a bit more than a .22mag+P.(if there were such a critter):wavey:

    OP I went with an LMT 10.5 because,according to people I know that own them, they are 100% reliable. The 11.5 wouldn't have been too bad, but the LaRue OBR 12" that I was looking at looked almost as long as an M4. I wanted a short SBR since I already have 16 and 20" barrels. If I were going for one all around rifle, I'd go with the 12" LaRue OBR.
     
    Last edited: Aug 21, 2012
  8. WoodenPlank

    WoodenPlank Who?

    7,958
    3
    May 15, 2010
    NW Florida
    Fair point, and agreed. Digging the HK sights on there, by the way.

    Also, obligatory: Oink. :pig:

    I believe that 75gr TAP T2 (P/N: 8126N) chronos somewhere around 2450-2500FPS from a 10.5", and is listed by Hornady as ~2650 from a 14.5".

    Reliable frag range on the 75-77 grain ammo is roughly 50 yards from a 10.5" barrel, slightly longer from an 11.5". Doesn't mean I'd want to be hit with one at ANY distance, though.

    I also know a couple guys that have made hits on steel poppers at 550 with 10.5" Mk. 18s and ACOGs, and a couple that have made hits at that range in combat. It's certainly not the ideal use of the platform, but it can be done in a pinch.

    Now if only I could find a source for 70gr TSX loads that weren't ass expensive... :crying:
     
  9. KML

    KML Millennium Member

    298
    1
    Sep 11, 1999
    Two years ago I went 11.5 so I could use a suppressor.At that time Gemtech would not replaced or warrant against baffle strikes in a 10.5,11.5 was as short as they would go.
     
  10. KalashniKEV

    KalashniKEV

    6,391
    3
    Sep 24, 2003
    NoVA
    I have 2 x 11.5s (KISS and my go-to) and just arrived at the same conclusion as Mark LaRue and John Noveske- 12.5" is the way to go for an all around, general purpose rifle.

    I have a Crusader Switchblock that should be here by the end of the week...

    It's not mine I just was showing a KX3 on a 7" upper... but yeah, the HK diopters are cool!
     
  11. Travclem

    Travclem Badass Member Lifetime Member

    6,775
    11
    Aug 4, 2008
    Lubbock, TX
    My load uses the 75gr Hornady OTM over 25.3gr H335 and CCI #41. it should be similar to the TAP5.56 performance.