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-   -   6.8 spc ll build questions (http://www.firearmstalk.com/forums/f20/6-8-spc-ll-build-questions-98071/)

dwmiller 10-03-2013 02:49 AM

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. ;)

dwmiller 10-04-2013 10:02 PM

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-mm-spc-cartridge-history-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.

dwmiller 10-12-2013 09:28 PM

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. ;)

AndyRexia 10-13-2013 12:09 AM

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 :-)

TheSadPanda 10-13-2013 07:19 PM

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.

1911love 10-14-2013 12:51 AM

What's the difference between spc and spcII?

Gatoragn 10-14-2013 01:04 AM

Quote:

Originally Posted by 1911love (Post 1400759)
What's the difference between spc and spcII?

Different chamber specs. Sorry I cannot quote them verbatim.

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

1911love 10-14-2013 01:33 AM

Quote:

Originally Posted by Gatoragn (Post 1400783)

Different chamber specs. Sorry I cannot quote them verbatim.

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

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?

TheSadPanda 10-14-2013 03:18 AM

Quote:

Originally Posted by 1911love
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?

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.

1911love 10-14-2013 03:58 AM

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


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