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Discussion Starter · #1 ·
I am contemplating buying an XCR, mostly b/c of the better bolt than what's found in the ARs.

I am particularly interested in a 6.8 conversion after initially purchasing the 5.56.

However, I notice there are only 10:1 twist bbls currently available for 6.8 and no reference to the groove number.

Will a 11:1 or 12:1 and 3-4 groove bbl be offered in the not too distant future? It seems these are the preferred specs for getting the most of the 6.8 cartridge with the SPC II or DMR chambers.

Thanks,
Sean King
Mesa, AZ
 

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Discussion Starter · #2 ·
I am contemplating buying an XCR, mostly b/c of the better bolt than what's found in the ARs.

I am particularly interested in a 6.8 conversion after initially purchasing the 5.56.

However, I notice there are only 10:1 twist bbls currently available for 6.8 and no reference to the groove number.

Will a 11:1 or 12:1 and 3-4 groove bbl be offered in the not too distant future? It seems these are the preferred specs for getting the most of the 6.8 cartridge with the SPC II or DMR chambers.

Thanks,
Sean King
Mesa, AZ
Oh, and is there any chance of a lightweight bbl instead of the HBAR? I don't see any real advantage to HBAR for most shooting I do and a big disadvantage in terms of weight.
 

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Sean,

Though I haven't tried shooting the SSA Combat load out of my 6.8 I really don't know what more it is going to give me that mine doesn't do right now. Before I cut the barrel down I was easily shooting 1" at 100m with the SSA OTM (at 2600+ FPS). Even with my 11" barrel I can still manage 2" groups all day long. If they came out with it I may buy it just to have a 16" barrel again but I am not convinced that it would do much more for me, at least not right now.
 

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Discussion Starter · #5 ·
I have a 10.5" LWRC 6.8 SPC with the 6 groove, 10:1 twist, SPC II chamber. In an SBR, the 10:1 twist is okay, but from the research going on with the 6.8 round, the 11:1 or even 12:1 with 3 or 4 grooves is yeilding lower pressures and higher velocities meaning you can get hotter loads without doing damage to the gun. SBRs are already known for being harder on components. Anything to slow that down a little is probably a good thing.

It's simply a matter of trying to find the best match to the cartridge....which is why I asked the question. After all, since I haven't bought one yet, I'd like it to have the best possible set of features.

I certainly don't plan to change out my 10.5" CHF "polygonal" rifled LWRC bbl b/c it's 10:1 and 6 groove, but I would have preferred a 11:1 or 12:1 w/ 3-4 grooves instead.

JMO,
Sean
 

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That makes sense. I am all about getting the best thing available. I know as more people have 6.8 guns that more testing is being done to figure out what works best. When Robarms released theirs (or finalized the barrel design) lots of this testing wasn't out there.

I personally am not looking for going hotter as I haven't seen a need to. Once I finish up all this SSA that I have and start reloading I may figure out that I wont be able to do what I want with my current setup. I would buy another 16" barrel if they released one.
 

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Discussion Starter · #7 ·
That makes sense. I am all about getting the best thing available. I know as more people have 6.8 guns that more testing is being done to figure out what works best. When Robarms released theirs (or finalized the barrel design) lots of this testing wasn't out there.

I personally am not looking for going hotter as I haven't seen a need to. Once I finish up all this SSA that I have and start reloading I may figure out that I wont be able to do what I want with my current setup. I would buy another 16" barrel if they released one.
I hear you on that....I have some of the lighter SSA loads and holy cow, this stuff is WAAAAY hotter than 5.56. I'm amazed at the punch 6.8 packs. I can only imagine what it does in the hottest "combat" loadings they now have.

Sean
 

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6.8 is a fantastic round no matter what load or barrel. I am extremely happy with my 6.8, 1:10 XCR barrel! However, I'm all for improvement. From what I have read, there is no downside to a 1:11 twist, but it gains the ability to use hotter loads and reduce pressure.
In any case, I wish 6.8mm in any format was general issue for our soldiers in harm's way. I'm sure its capabilities would save some lives on our side.
 
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I was just on the SSA website and noticed that the MINIMUM requirements for the "combat loads" are a type II chamber with a 1-10 twist barrel and a 6 groove barrel.

Isnt that what RA has in the XCR?

And if they are getting safe pressures at 1-10 then why would we go out of the way to get a 1-11 twist to shoot this stuff!?!? ???
 

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Yes, I believe those are the specs for the XCR barrel. i can't be sure on the grooves though, for some reason 5 grooves keeps popping into my mind.
 

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Art at SSA posted that 10 twist SPCII requirement to purchase "combat" ammo so all the guys with LWRCs would buy his ammo.
some work some don't.
I hear good things come to those that wait ;D You guys hang tight with the XCR
 

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Discussion Starter · #16 ·

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Discussion Starter · #17 ·
I was just on the SSA website and noticed that the MINIMUM requirements for the "combat loads" are a type II chamber with a 1-10 twist barrel and a 6 groove barrel.

Isnt that what RA has in the XCR?

And if they are getting safe pressures at 1-10 then why would we go out of the way to get a 1-11 twist to shoot this stuff!?!? ???




B/c the 1:11 (and 1:12/13) have even more potential for hotter loads without pressure signs. I have a 1:10 LWRC with the polygonal rifled CHF bbl....it works too, but 1:11 or 1:12 is even better.

Sean
 
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After reading up on this a little more it does appear that the original design called for a 1-12 (maybe 1-11) IIRC, apparently the reason for using the 1-10 was because they had barrels from 270's that were used initially.

I agree that if we are gonna make it, lets make it to spec rather than follow the crowd and just blindly make 1-10 because thats what some other company is using.
 

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We started working on improving the 6.8 3 years ago when we thought the military may adopt it. We just thought that if it performed better it would be more appealing.
So 3 years later we are getting 2-300fps more from the same round and the same length barrels.
That means that the terminal range has been increased by apx 100 yds. using the fact that most bullets need 1700fps to expand or provide adequate terminal performance.
You could also look at it like 8" barrels lose apx 200 fps to a 16" barrel so now an 8" barrel will give the same terminal performance that a 16" did 3 years ago.
We are able to load over the counter powders that give us more velocity with less pressure than the current loads SSA is using.
2850fps from a 110gr bullet shot out of a 20" barrel is normal with 12 and 13 twist and even a 11.25 twist Lothar Polygonal barrel I have. My 12 twist 3 groove barrels will allow 30.8gr of 10X, 32gr of H322 and 33gr of H335 behind 110gr bullets and have produced 2950fps from a 20" barrel, 32.5gr of 10 x and 90gr TNTs will hit 3158fps.DO NOT try that in the average barrel.
These velocities are what promted the call to Alex a few months ago, I was hoping he could go to the trials with new barrel specs and open a few eyes. I would like to see him take some contracts away from the big boys but, knowing how our goverment works I think they would just steal his design and give it to one of the companies that have benefits for those making the decision.
After all isn't that how KAC ended up with the 308 contract?
Good luck at the trials and don't forget the blank firing attachment ;)
 

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6.8 has come a long way in a short time.

FYI, Constructor is THE go-to guy for 6.8 info.

Thanks for your posts here constructor! Keep 'em comming!
 
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