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Thoughts on fast twist 6.8 SPC barrel

Discussion in 'Rifle Country' started by KansasPaul, Nov 15, 2012.

  1. KansasPaul

    KansasPaul Well-Known Member

    I am contemplating the build of a 6.8SPC rifle. Most rifles of this caliber have a 1:10 or 1:11 twist. However, Bison Arms is manufacturing a barrel that has a 1:7 twist, designed for heavy bullets at sub-sonic velocities but according can shoot light bullets? I have limited knowledge of this round and welcome any input. I sure don't want to shell out a stack of dollars only to find out the the set-up doesn't work. I've exploring this as a platform that could be used to shoot p-dogs (light bullets), coyote (light bullets) and deer (heavy bullets, close in).

    I welcome any opinions & experiences with this round.

  2. Owen Sparks

    Owen Sparks member

    The slower twist was developed along with the now standard Spec II chamber in order to lower pressure and allow higher velocity loadings. Unless you are building a special purpose suppressed six 8 designed to shoot very heavy subsonic loads you will be limiting your ammo options. Some high performance factory loads such as those offered by Silver State Armory are not recommended for fast twist barrels because of pressure issues.
  3. Owen Sparks

    Owen Sparks member

    Let me add this, the six 8 cartridge was designed to fit into the limited space of a standard AR sized magazine. That limits over all cartridge length to that of the 5.56 round. This means that when you try to load bullet heavier than around 120 grains it will severely limit powder capacity and therefore velocity. Also, the longer, heavier .277” bullets of 130 grains or more were designed to perform at supersonic .270 velocities.

    If you really need a supressed rifle firing a subsonic round there are better caliber choices than an over bulleted six 8.
  4. 68wj

    68wj Well-Known Member

    Bison's 1/7 twist barrel (BSP) was designed to shoot full velocity loads and up to 200 grain subsonics. If you dont plan on shooting subsonics, I would stick with the slower twist. However, since they paid attention to the land/groove profile and chamber, I shot 100 grain (warm) handloads and was perfectly accurate at the 200 yard limit on the range with a BSP.
  5. Owen Sparks

    Owen Sparks member

    A 200 grain bullet designed for .270 velocity will behave like a full metal jacket at subsonic velocity and zip through an animal with minimal damage.
  6. 68wj

    68wj Well-Known Member

    Sure, but most rifle bullets wont expand subsonic from any cartridge. It is a long bullet that is barely stable and should tumble rather quickly though. Regardless, I think subsonic is a poor choice for hunting but have seen multiple examples of it working fine.
  7. KansasPaul

    KansasPaul Well-Known Member

    It may be that I am asking too much of this configuration. I like the AR platform especially in a light weight configuration. I would like to have one rifle that will pull multiple duty. When I chose my last 5.56 AR I went with a faster twist so that it would handle heavy bullets. I suppose that what I was considering with the 6.8 and a fast twist was comparable to my 5.56. I am unsure if I would truly suppress the rifle although shooting subsonic loads unsuppressed would still likely be viewed as favorable by my neighbors (again the assumption is that subsonic loads are much quieter than standard loadings).

    As mentioned, I can't afford (financially) to make a mistake considering the cost of these things. Initially I considered going in the 6.5 Grendel direction but got off on a bunny trail when I learned about the faster twist offering in the 6.8.

    I do appreciate the input!!


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