COBrien's 6.8 SPC Build

[COBrien]

This isn't really a "build thread," since it's already built, but anyhow...

In keeping with my stubborn habit of being about 10 years behind the curve when it comes to calibers and/or rifles, I decided to build myself an "alternate caliber" AR upper.

In 6.8 SPC II.

I was looking for a good all-around caliber that'd do everything better than a 5.56, but without needing to resort to a 20+" barrel to get decent velocities. And I landed on the 6.8.

So, without further ado, here's the parts list:

AR-15 Performance 16" Socom barrel, 1:11.25" 3R rifling, mid-gas;
AR-15 Performance "Super Bolt";
USGI M16 Parkerized/chromed bolt carrier;
Larue SAT 13.2" handguard;
Faxon gas block w/ nitrided gas tube (will probably be swapping it out for an SLR adjustable, but wanted to get it running first...);
and, of course, a Griffin 30SD muzzle brake.

This will all be at home on my A2 lower that I built for my Dissipator, at least for the time being. I may end up putting together a lower with a carbine buttstock at some point in the future, but who knows.

Also, my Leupold VX-HOG is riding on this upper for now. I robbed it off my Tavor 7, which will soon be getting a PA 5x prism.

I'm excited to get this thing out to the range and see how she shoots.

No comments on the state of my workbench...🤣

[shooterrex]

Hope it shoots well for you. Doesn't everyone's bench look like that?

[Armed Eye Doc]

6 hours ago, COBrien said:

No comments on the state of my workbench...🤣

 

53 minutes ago, shooterrex said:

Hope it shoots well for you. Doesn't everyone's bench look like that?

I wondered why he cleaned it off so much.  Happy shooting. 

[Radioactive]

7 hours ago, COBrien said:

This isn't really a "build thread," since it's already built, but anyhow...

In keeping with my stubborn habit of being about 10 years behind the curve when it comes to calibers and/or rifles, I decided to build myself an "alternate caliber" AR upper.

In 6.8 SPC II.

I was looking for a good all-around caliber that'd do everything better than a 5.56, but without needing to resort to a 20+" barrel to get decent velocities. And I landed on the 6.8.

So, without further ado, here's the parts list:

AR-15 Performance 16" Socom barrel, 1:11.25" 3R rifling, mid-gas;
AR-15 Performance "Super Bolt";
USGI M16 Parkerized/chromed bolt carrier;
Larue SAT 13.2" handguard;
Faxon gas block w/ nitrided gas tube (will probably be swapping it out for an SLR adjustable, but wanted to get it running first...);
and, of course, a Griffin 30SD muzzle brake.

This will all be at home on my A2 lower that I built for my Dissipator, at least for the time being. I may end up putting together a lower with a carbine buttstock at some point in the future, but who knows.

Also, my Leupold VX-HOG is riding on this upper for now. I robbed it off my Tavor 7, which will soon be getting a PA 5x prism.

I'm excited to get this thing out to the range and see how she shoots.

No comments on the state of my workbench...🤣

My clean bench looks just as bad. I wanted a 6.8 for hogs but just couldn’t pull the trigger. May go 6mm arc after we see how it all shakes out or a grendel. 

[dpete]

1 hour ago, Radioactive said:

May go 6mm arc after we see how it all shakes out or a grendel. 

As was said over on the Grendel forum.

The difference between a Grendel and a 6mm ARC is:

A grendel is more of a hunting caliber you can target shoot with.

A 6mm ARC is more a target caliber you can hunt with.

[Radioactive]

I think any of the 3 will kill hogs nicely.

[98Z5V]

 

9 hours ago, COBrien said:

...

NICE!   How long did that handguard take?  First one I've seen in the wild, since they released them.

The PA 5x prisms are on sale right now, got the email yesterday.  

[COBrien]

1 hour ago, 98Z5V said:

 

NICE!   How long did that handguard take?  First one I've seen in the wild, since they released them.

The PA 5x prisms are on sale right now, got the email yesterday.  

I think it took them 2-3 days to get it shipped out. Since I’m in OK, once it leaves their place, I get it in 2 days. 
 

The mounting system is different, but it’s rock-fvckin-solid. I don’t consider myself a fanboi, but for the money you can’t beat the quality of this handguard. 
 

On a side note, I took this rifle by the gun shop the other day. My buddy/pusher/PRS snob who tried talking me out of a 6.8 became extremely interested when I started telling him about the rounds Druid Hill Armory is putting out...
 

90 gr Gold Dots @ 3,088 FPS, 100 gr LeHigh Controlled Chaos @ 2,845, 110 gr V-Max @ 2,757. All loaded to actual SPC II specs, not the original SAAMI SPC spec. 

He’s pushing a 6 BR or 6 CM at those speeds out of a 22-24” barrel, so I now have his attention. 

He now wants to get behind this rifle and walk it out to 1,000 yards. We’ll see...

Here’s a slightly less sh!tty pic, taken after I got the kids to bed. 

Edited September 18, 2020 by COBrien

[COBrien]

2 hours ago, 98Z5V said:

The PA 5x prisms are on sale right now, got the email yesterday.  

I just checked the website, and they’re still showing $329.99. Optics Planet has them for $329.49, plus a 7% discount for reviewing a product. 
 

Now that I think about it, I haven’t been getting emails from PA. Gonna need to look into that...

[98Z5V]

42 minutes ago, COBrien said:

The mounting system is different, but it’s rock-fvckin-solid.

Same mounting system as the standard LaRue rails - and it IS rock solid.  Very, very similar to the PRI mounting system, which is equally as solid.  There's nothing better on the market outside of those two, as far as heavy-duty goes.  I'd rate the older Daniel Defense mounting system a very close runner up to those two - and that's the old DD  5.56 RIS II setups and the original .308 setup (7.62 LITE Rail) - the 6-bolt designs.  I'd favor the LaRue setup as having a slight edge (or slightly "improved') over the PRI setup.  It's a badass solid lockup, that's for damn sure.  Those 3 are the top of my list, as far as "smart mounting" goes - they all nailed it. 

[COBrien]

9 hours ago, 98Z5V said:

Same mounting system as the standard LaRue rails - and it IS rock solid.  Very, very similar to the PRI mounting system, which is equally as solid.  There's nothing better on the market outside of those two, as far as heavy-duty goes.  I'd rate the older Daniel Defense mounting system a very close runner up to those two - and that's the old DD  5.56 RIS II setups and the original .308 setup (7.62 LITE Rail) - the 6-bolt designs.  I'd favor the LaRue setup as having a slight edge (or slightly "improved') over the PRI setup.  It's a badass solid lockup, that's for damn sure.  Those 3 are the top of my list, as far as "smart mounting" goes - they all nailed it. 

I've never handled a PRI or DD rail, but I do know they both have a reputation of being stout.

I guess it makes sense, then, that I had to pick up a PRI barrel nut wrench to install the LaRue rail. None of my other wrenches had pins that were long enough to reach the gas tube holes, once the barrel nut got down into the knurled "retaining ring," for lack of a better term.

I'm extremely happy with how this build came out, and I can't wait to get it to the range. I swapped out the weight on my Armaspec SRS to a standard C weight last night, so now all I need to do is give her a quick strip and once-over with some Ballistol, then run some patches down the bore.

[MikedaddyH]

That is one beautiful rifle , handguard looks great. 16" to 18" barrel is all you need from this caliber. The 115gr projectiles worked the best for me, the lighter ones would open up in groups (110gr) the 90grain bullets were fast but I had a lot of flyer's. Hornady 120's were the most accurate round but I had a hard time finding more of them. Also get/use a H3 buffer ! Have fun with your new toy 👍

Edited September 18, 2020 by MikedaddyH

[COBrien]

10 minutes ago, MikedaddyH said:

That is one beautiful rifle , handguard looks great. 16" to 18" barrel is all you need from this caliber. The 115gr projectiles worked the best for me, the lighter ones would open up in groups (110gr) the 90grain bullets were fast but I had a lot of flyer's. Hornady 120's were the most accurate round but I had a hard time finding more of them. Also get/use a H3 buffer ! Have fun with your new toy 👍

Thanks for the tips and kind words, Mike!

After talking to Harrison @ AR-15 Performance, he strongly suggested a C buffer and spring on his barrels. Said the gas ports are specifically sized with a C buffer in mind. Having said that, I have C, H, and H3 weights for the SRS. We'll fine-tune it and see what she prefers. When I get it running like I want without a can, I'll see how it runs with the can mounted. Will probably be springing for an SLR adjustable gas block at that point...

As far as ammo, I have some 60 rounds of Hornady Black 110 gr V-Max on hand. And my 100 gr. Controlled Chaos arrived today. Then I got a PM from a guy at the 68forum saying he had 80 rounds of 90 gr Gold Dots from Druid Hill Armory that he'd sell me. Suddenly, I'm somewhat flush with 6.8 ammo!

Edited September 18, 2020 by COBrien

[MikedaddyH]

Just looked at the picture again... Rifle Buttstock !! Ok ! Did a adjustable gas block on one, not really necessary.

[COBrien]

The rifle buttstock part really doesn't play in, though. I'm running the Armaspec Stealth Recoil Spring with a Delrin spacer behind it to accommodate the rifle-length buffer tube. Shouldn't function any differently than in a carbine tube, right?

My thought on the adjustable gas block is just to keep it from being over-gassed when suppressed. Maybe it won't be necessary, but I won't be paying that $110 until I find out it is. Lol!

[Rsquared]

20 hours ago, COBrien said:

That is one SEXY rifle!

[unforgiven]

On 9/17/2020 at 12:05 PM, COBrien said:

This isn't really a "build thread," since it's already built, but anyhow...

In keeping with my stubborn habit of being about 10 years behind the curve when it comes to calibers and/or rifles, I decided to build myself an "alternate caliber" AR upper.

In 6.8 SPC II.

I was looking for a good all-around caliber that'd do everything better than a 5.56, but without needing to resort to a 20+" barrel to get decent velocities. And I landed on the 6.8.

So, without further ado, here's the parts list:

AR-15 Performance 16" Socom barrel, 1:11.25" 3R rifling, mid-gas;
AR-15 Performance "Super Bolt";
USGI M16 Parkerized/chromed bolt carrier;
Larue SAT 13.2" handguard;
Faxon gas block w/ nitrided gas tube (will probably be swapping it out for an SLR adjustable, but wanted to get it running first...);
and, of course, a Griffin 30SD muzzle brake.

This will all be at home on my A2 lower that I built for my Dissipator, at least for the time being. I may end up putting together a lower with a carbine buttstock at some point in the future, but who knows.

Also, my Leupold VX-HOG is riding on this upper for now. I robbed it off my Tavor 7, which will soon be getting a PA 5x prism.

I'm excited to get this thing out to the range and see how she shoots.

No comments on the state of my workbench...🤣

Nice job brother 👍

[98Z5V]

10 hours ago, COBrien said:

After talking to Harrison @ AR-15 Performance, he strongly suggested a C buffer and spring on his barrels. Said the gas ports are specifically sized with a C buffer in mind. Having said that, I have C, H, and H3 weights for the SRS. We'll fine-tune it and see what she prefers. When I get it running like I want without a can, I'll see how it runs with the can mounted. Will probably be springing for an SLR adjustable gas block at that point...

 

You just severely Complicated Shiit With Complicated Shiit.  I'll be interested to see how this works out, in the long run. 

[COBrien]

6 hours ago, 98Z5V said:

You just severely Complicated Shiit With Complicated Shiit.  I'll be interested to see how this works out, in the long run. 

I was waiting for you to say that...

The SRS C is comparable to a 3.3 oz. buffer, so that shouldn’t complicate things. Right? Lol!

I’m running a non-adjustable gas block for now, and will make changes one at a time. Also not complicated, right?

🤣

[98Z5V]

On 9/19/2020 at 6:51 AM, COBrien said:

I was waiting for you to say that...

You're now making a Race Gun, brother.  It's gonna run GREAT...   on that one load that it likes.  As soon as you try other ammo - it might work, it might not.  It might choke...   That's cool, if you're handloading that ONE load all the time, though.  God forbid you need some other ammo, at some other time...

 

Race Guns have their place.  They're not guns to depend on, if you ever need to vary your load for any reason - they're gonna choke. 

If he "tailored" his gas system for that specific lightass buffer - it means he made his gas port smaller.  3.3oz buffer isn't even the H1 (3.8oz) buffer that all these guys ship in "factory guns" - that doesn't work worth a shiit...   Hmmm...   Ponder that, before you run all the complicated parts...  Think about what you really want this gun to do, and select parts from that point - purpose of the gun, in it's first place.  

It takes a3.8oz H1 buffer to make the M4A1 fully-functional.  And that's just a 5.56 gun.  6.8 SPC is a different animal.  On to another "different animal," - my .224 Valk is based on a 6.8SPC case, directly, necked down to .224.  That thing needs a VLTOR A5H2 buffer to run right, and not beat me up.  That's 5.33oz.  It "runs" with a VLTOR A5H1, which is 4.56oz, and it's a HARSH recoil impulse from it...   I'll be switching out all my VLTOR A5H2 buffers, that weigh that, for Slash's VLTOR buffer, his A5H3 buffer, that weighs 5.5oz.  It's just smoother, with his buffer...   My $0.02 on the whole affair.

That's gotta be one small-ass gas port in that 6.8 barrel...  

Edited September 21, 2020 by 98Z5V

[COBrien]

25 minutes ago, 98Z5V said:

You're now making a Race Gun, brother.  It's gonna run GREAT...   on that one load that it likes.  As soon as you try other ammo - it might work, it might not.  It might choke...   That's cool, if you're handloading that ONE load all the time, though.  God forbid you need some other ammo, at some other time...

 

Race Guns have their place.  They're not guns to depend on, if you ever need to vary your load for any reason - they're gonna choke. 

If he "tailored" his gas system for that specific lightass buffer - it means he made his gas port smaller.  3.3oz buffer isn't even the H1 (3.8oz) buffer that all these guys ship in "factory guns" - that doesn't work worth a shiit...   Hmmm...   Ponder that, before you run all the complicated parts...  Think about what you really want this gun to do, and select parts from that point - purpose of the gun, in it's first place.  

It takes a3.8oz H1 buffer to make the M4A1 fully-functional.  And that's just a 5.56 gun.  6.8 SPC is a different animal.  On to another "different animal," - my .224 Valk is based on a 6.8SPC case, directly, necked down to .224.  That thing needs a VLTOR A5H2 buffer to run right, and not beat me up.  That's 5.33oz.  It "runs" with a VLTOR A5H1, which is 4.56oz, and it's a HARSH recoil impulse from it...   I'll be switching out all my VLTOR A5H2 buffers, that weigh that, for Slash's VLTOR buffer, his A5H3 buffer, that weighs 5.5oz.  It's just smoother, with his buffer...   My $0.02 on the whole affair.

That's gotta be one small-ass gas port in that 6.8 barrel...  

Fair point, and well taken. It’s gonna take some fiddling with (as have all my builds thus far...), but I’m good with that. 
 

One added complication is that I’d like to find the combination that’ll work both with this 6.8 upper AND my 5.56 Dissipator upper (if there is such a combination). 
 

Ultimately I will be building another lower for the 6.8. But, for now, this’ll have to do. 

[98Z5V]

1 minute ago, COBrien said:

One added complication is that I’d like to find the combination that’ll work both with this 6.8 upper AND my 5.56 Dissipator upper (if there is such a combination).

See?....    NOW YOU DID IT!!!...   

You just made this MORE COMPLICATED with that statement...  

We'll help - with what we can.  I promise you that much, brother...  

[COBrien]

On 9/20/2020 at 10:21 PM, 98Z5V said:

See?....    NOW YOU DID IT!!!...   

You just made this MORE COMPLICATED with that statement...  

We'll help - with what we can.  I promise you that much, brother...  

I know, and I appreciate it.

As easily as this upper went together (once I got ahold of some barrel nut shims...), I'm hoping the trend will continue when it comes time to get it running.

But Murphy and I have been very close friends for a long, long time. I'm sure he'll find some excuse to show up.

[Rsquared]

8 hours ago, COBrien said:

But Murphy and I have been very close friends for a long, long time. I'm sure he'll find some excuse to show up.

That bastard has been bunking with me for a long time. Can't seem to shake his ass.

[Cunuckgaucho]

Seem Murphy is a slut of the highest order with the lowest standards...

I hear there are some out there that feel Murphy is an optimist