6.8 spc ll build questions

Discussion in 'AR-15 Discussion' started by dwmiller, Oct 2, 2013.

  1. dwmiller

    dwmiller Well-Known Member

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    Hey, got a question for the experts. I'm in the middle of a new 6.8 20" rifle build. I am leaning toward the yhm barrel but I've noticed the twist rates vary a bunch in this caliber. I've seen everything from 1-8.5 to 1-12 depending on the manufacter. Can someone give me a little guidance on correct twist for this caliber?

    Barrel in question is YHM-88-F 20" fluted chrome lined barrel with a 1-10 twist rate. I'm guessing that Yankee Hill probably is the standard twist.

    New to the caliber but it's my 41st AR build. I don't need general build advice just caliber specific info. ;)
     
    Last edited: Oct 2, 2013
  2. dwmiller

    dwmiller Well-Known Member

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    Well change of plans, I found a 16" 6.8 SPC II barrel with a 1-10 twist for $125 + shipping. Barrel is threaded 1/2-36 which is a little odd (1/2-36 is standard for the 9mm). Looks like I'll be firing up the lathe to make a custom comp when this comes in, but at that price its half the YHM barrel.

    I went through and read all the info I could find last night and pretty well answered my twist rate questions. Turns out that lots of different twists were tried during design and 1-10 won out as the standard for 110 grain bullets. Also turns out that the 6.8 is designed around short barrels and is optimum at 16" and shorter. Probably saved 1.5 lbs off my build. Goodby long rifle, hello sweet carbine deerslayer. :D

    Thanks all for the PM's with the links. Here are the ones that helped me make my decision.

    http://en.wikipedia.org/wiki/6.8_mm_Remington_SPC
    http://demigodllc.com/articles/6.8-...ry-development-hornady-stag-arms-carbine/?p=1
    http://68forums.com/forums/forum.php?
    ^^^^definitely check this forum out if you are interested in this caliber.
     
    Last edited: Oct 4, 2013

  3. dwmiller

    dwmiller Well-Known Member

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    Ok barrel came in today. I'll get home next weekend and get the upper assembled. Hopefully my 6.8 mags from psa arrive before I get there. A little function testing fun and then strip it back down for duracoat. Desert digital with tan furniture sounds just about right for this rifle. ;)
     
  4. AndyRexia

    AndyRexia New Member

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    Sounds pretty cool man. Sorry but I know 0 about 6.8 so I don't have any advice for ya. I like the sound of it though and new builds are always exciting. Keep us posted and let's see some pics :)
     
  5. TheSadPanda

    TheSadPanda New Member

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    Good call on not going with a 20" barrel. You gain almost nothing FPS wise but you do gain a lot of weight. 16-18" is optimum for spcII barrels. Also, 1/10 and 1/11 are the two main twists for this cartridge. Either will work just fine and then some. They say that 1/11 is supposed to be better, but it all depends on the load, grainage, and all that jazz. I'm also working on a 6.8 build currently, so keep us (me in particular) updated on your build. I'm very interested to see what you do with it.
     
  6. 1911love

    1911love New Member

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    What's the difference between spc and spcII?
     
  7. Gatoragn

    Gatoragn Active Member

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    Different chamber specs. Sorry I cannot quote them verbatim.

    To convert a spcI to SpcIi, you have to ream the chamber.
     
  8. 1911love

    1911love New Member

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    I had no idea a new spec was out. So I'm guessing spcII is superior to spc? Can spc be fired from an spcII weapon?
     
  9. TheSadPanda

    TheSadPanda New Member

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    There were pressure and twist issues with the original SPC chamber. SPC II allows for a broader grain usage and better accuracy with those loads. SPC II Is rated for higher pressure loads, so it can shoot any original spc loads. The only loads you have to look out for are the high power tactical and hunting loads like the ones SSA offers. Those loads should never be fired in an original SPC chamber. You can technically get away with firing medium to low powered spcII ammo in an spc chamber, but is ill advised. It's not worth the risk.
     
  10. 1911love

    1911love New Member

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    Thanks Panda. Down the road I want to build an SPR in 6.8, now I know it's got to be spcII.
     
  11. Axxe55

    Axxe55 The Apocalypse Is Coming.....

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    i know this is the AR section, but wanted to pick up some information on the 6.8 SPC. gladi did, because i wasn't aware of the newer version the SPC II. very interesting.

    at some point i would like to build a bolt action rifle in the 6.8 SPC round.

    very informative guys. thanks.
     
  12. TheSadPanda

    TheSadPanda New Member

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    Almost all manufacturers have switched over to SPC II. so if buying anything new you should be fine. Buying anything used make sure you ask specifically. Right now the only bolt action i know of in 6.8 is R700 and it is stupid expensive.
     
  13. 1911love

    1911love New Member

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    Why would a 700 be stupid expensive? It's just a different short action caliber right?
     
  14. TheSadPanda

    TheSadPanda New Member

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    This starts getting into an area im not sure about, but from what I can tell they are discontinued from Ruger and Remington. They were only made for a year or two, so the number of them out there is minimal. You cold always do a barrel job but you would still need a 6.8 bolt face i think. That's all i could pick up on my quick research.
     
  15. Axxe55

    Axxe55 The Apocalypse Is Coming.....

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    i looked at Remingtons website and they offered it in the Model 7 platform. which is pretty much a short compact M700 action, but it's already been discontinued.

    would have to open up the bolt face on a 223 sized bolt to make it work. the bolt face on a 223 is 0.378 and the bolt face for the 6.8 is 0.422.
     
  16. dwmiller

    dwmiller Well-Known Member

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    Yeh I'll get home on Friday and get to unbox the parts I ordered.

    Choice of two free float handguards. I bought the new 13" utg single rail to try it out. Everyone that tried the shorter one out had good things to say about it. Also have a 12" psa quadrail in case I don't like it. I always preferred a single rail myself, at least on a hunting gun. At $100 bucks its worth a closer look. ;)

    Pics will come up as I unbox and test assemble the upper. ;)

    Anyone have any suggestions for a comp that is threaded 1/2-36? Not too many options that I found. May just make an adapter for 1/2-36 to 5/8-24. This seems to be becoming the standard thread for this caliber.
     
    Last edited: Oct 14, 2013
  17. Axxe55

    Axxe55 The Apocalypse Is Coming.....

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    seems like Brownell's had a few in that size.
     
  18. dwmiller

    dwmiller Well-Known Member

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    Wow, fast response!

    A "few" is right, three came up in the right caliber. Seven more in 9mm. And the YHM flash suppressor is the only one in stock. Really need a comp not a flash hider. Muzzle flip is supposed to be a little more severe than the 223. Heavier bullet weight, just makes sense that it has more recoil.

    Really hoping that someone was already making a hunting/target comp in my specs. If anyone can point me to a semi finished comp it would save me hours of machine work.
     
    Last edited: Oct 14, 2013
  19. Axxe55

    Axxe55 The Apocalypse Is Coming.....

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    here's a link to MidwayUSA. they also have a few that might be of interest to you.

    http://www.midwayusa.com/find?sortby=1&itemsperpage=24&newcategorydimensionid=17102
     
  20. dwmiller

    dwmiller Well-Known Member

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    Thanks for the info but the only 1/2-36 threaded they offer is the EGW's flash hiders, and both are out of stock. Problem is rare threaded barrel for this caliber. :(
    Guess I'll be running the lathe a night or two while I'm off. Need to order a 1/2-36 bottoming and starting dies before I get home.