6.8 SPC milspec upper assembly

5440fight said:
I believe that, because both rounds are equal length, normal mags will work. Please correct me if I'm wrong...
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I will try do this as gently as possible but that statment is not accurate. :)

I have done a tremdous amount of reseach and have built myself a functioning carbine using mostly Stag parts in 6.8 SPC (including a correctly marked lower).

To really understand this we need to back up a few steps. While the 6.8 Spc (bullet of 0.277 diameter) is of similar legnth to the 5.56 Nato, the parrent cartridge is actual 30 Rem, that has had the body taper "blown out", and necked down to 0.277. The result is a cartridge of similar length but its quite a bit fatter, with a larger case head. So the 6.8 bolt is acutally "open up" when you compare it to the 5.56 bolt head.

Orriginally the thought was that one should be able to simply change the follower of a METAL 5.56 Nato mag an go to town. However actual experience has show otherwise. What they found is due to the fatter body of the cartridge, what would happen is that, even with the changed follower, one would insert about 3 cartridges into the mag, and then it would bind, on the 4th round, one would buldge the mag.

What they found is that the longatudinal grove in a 5.56 mag (which give it added rigidity) were simply too deep. To solve this. 6.8 mags still have those longatudinal grooves, but they are much shallower to compesate for the larger body dimentions.

On another note, I spoke at length with the Justin at the techincal department over at Magpul, hoping that they would produce Pmags in the 6.8 caliber. The reuslt was that, using polymer constrction, Magpul is not able to get the wall of the mag thin enough, to fit in a normal AR mag well, with retaining the strength neccesary to have a robust mag. So the long in the short of it is, that we will probably not see pmags for the 6.8

The up side of this however is that most mags for 6.8 are actually made out of stainless steel.

Hope this helps, and would be happy to do my best to field any other questions you might have.

regards and all the best

AbH
 
Paulinski said:
Richard nailed it.

You need a 6.8 specific mag and barrel with 6.8mm SPC MOD 1 Chamber (.100 Freebore) if you want to shoot the hot 6.8 loads.
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Paulinski:

Thx for the Kudo's, however I did not know about the Mod 1 chamber. Something to keep in mind.

Another thing to note, is that while they started with a 1-10 twist, they have now gone with a 1-11 twist, to reduce preasure and improve preformance.

regards

AbH
 
hm... would 5.56 happen to fit and feed in those SS 5 round 6.8mm magazines? If you catch my drift.

(1) Any cartridge magazine

(a) that is capable of containing more than five cartridges of the type for which the magazine was originally designed and that is designed or manufactured for use in
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Would fall under the same 'LAR-15 mag' loophole.
 
While I have not tried it I would think not.

First you would need to change the follower (quite a bit different than 5.56)

Second, I am not sure how thoes 5.56 rounds would behave in the larger space afforeded them by the reduced groove depth

Third, 5.56 mags on the whole are cheaper and more plentiful than 6.8 mags.

Just my 2 cents. YMMV

reards

AbH
 
What Richard said on the mags....

Paul, I've never heard of a 6.8 Mod 1 chamber, is that a manufacturers name for the SPC II maybe?

I know Stag is using the new(er) 6.8 SPC II chamber, which I am told differs from the SAAMI 6.8 chamber by the addition of .100" freebore, for loadings beyond 6.8SPC SAAMI pressure (which basically means SSA military ammo). Also has the 1/11 twist. Same thing?
 
patricktj said:
i`m look for a 6.8,i replace only the barrel and mag on the 5.56 ar15 set up
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The above statment again is Not accurate. The 6.8 spesific components are, in my understanding:

  • bolt
  • barrel
  • mags

However, When most look at a 6.8 they usually get an entrie top end and mags.

Gents, remember free advice is whorth what you paid for it.

YMMV

regards

AbH
 
dangertree said:
What Richard said on the mags....

Paul, I've never heard of a 6.8 Mod 1 chamber, is that a manufacturers name for the SPC II maybe?

I know Stag is using the new(er) 6.8 SPC II chamber, which I am told differs from the SAAMI 6.8 chamber by the addition of .100" freebore, for loadings beyond 6.8SPC SAAMI pressure (which basically means SSA military ammo). Also has the 1/11 twist. Same thing?
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Yes its the same thing.

I'm waiting for Noveske to get caught up with their 14.5 and 16" barrels to dive into my 6.8 project.
 
So from what I understand, as long as I have a complete 6.8 SPC upper, bolt assembly and mag, I'm good to go using any milspec AR-15 lower.
 
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