Lightweight 6.5 CM project

[MSTN]

I've been amazed at how well a sub-five pound AR' will shoot, both in terms of reliability as well as accuracy. But how about a big block gas gun? Can they be made to run reliably, accurately, safely, at the reduced weights made possible by new and innovative components?

Based on my first attempt, I'm encouraged.

The foundation of this latest project is a 16 ounce 2A Armament .308 Xanthos billet receiver set. 16 ounce! 2A hogs out every possible nook and cranny to get this package as light as possible. Typical AR-15 receiver sets weigh 20% more than this. The 2A 15" forend with its titanium barrel nut weighs in under 10 ounces. The heart of the gun, a 22" +2 PROOF Research barrel comes in at just 44 ounces. This barrel is GORGEOUS inside! Looking down it with a borescope reveals just how good a PROOF barrel is in terms of final surface finishing treatments. No one does a throat like this.

While I was interested in saving weight, I was not interested merely building the lightest gun possible. I want it to be accurate. So, I went with a full mass JP bolt carrier for reliability & accuracy and fairly heavy Magpul STR buttstock for the superlative cheek weld. Even then, the bare rifle weighs just 8 pounds 2 ounces. I could knock half a pound off of this by simply going with a Mission First Tactical (MFT) stock. plus another quarter pound going with a low mass carrier.

This rifle has all V Seven titanium parts wherever applicable. I went with a steel SLR adjustable gas block because I was just too impatient to wait for a titanium one to come in from SLR. A Geissele National Match trigger simplifies trigger control, breaking at a crisp 2.5 LB. And a PRI Gas Buster is there to keep the gas out of the shooter's face.

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[The King]

How does it shoot sir...how does it shoot?

 

[MSTN]

I have had only one brief range session with the completed rifle.
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Only a few rounds were required to dial in the superlative Kahles K624i scope in its Spuhr cantilever mount at 100 yards. What a simple task it is to set the zero stop with this scope! I love the SKMR-1 reticle, too.

Then, the next step was to begin dialing in the gas with the SLR adjustable gas block. The Thunder Beast Ultra 7 is the first suppressor I'm trying on this rifle. They are known to be superbly accurate and very quiet (plus extremely lightweight at only 9.7 ounces). But, they do produce a lot of back pressure for a gas gun shooting such a high pressure cartridge, making an adjustable gas block a must. So, I started with the gas dialed down to half closed. Brass was ejecting to my 2:30, so I went two clicks further closed. Then, the brass ejected to what most feel is optimum, the shooter's 4 o'clock.

That being said, there is another variable in play that strongly affects the direction ejected brass takes, and that is the angle on the face of the brass deflector. They're not all the same, and those on 2A Armament uppers are decidedly unique.

Next, I actually want to find the point at which the rifle will eject but not lock the bolt to the rear on an empty chamber. Then, I'll open the gas block back up a couple of clicks and leave it there, and not worry too much about the direction of the ejected brass. This means I'm not really finished adjusting the gas block for use with the suppressor. And I have not even fired a single unsuppressed round yet.

Why did I stop my tinkering here? If you guessed I wanted to just enjoy shooting it, you are correct.

This is a fairly light rifle: 8 LB, 2 OZ naked, and 12 LB 7 OZ with scope, mount, and magazine. It moves around a little under recoil, but it is not unpleasant. I'm still trying to get accustomed to it. Off a concrete bench with a bipod and rear bag, my worst five shot group (the first) was just over an inch. My best was under half an inch. I'd say they averaged right about 3/4". I'm not exactly famous for my shooting off the bench, however.

Keep in mind that this was the first outing with the rifle, with a new barrel, with one brand of commercial ammo. Really fantastic stuff, though - Prime 130. I should point out that with 50 rounds through the new rifle, there were zero malfunctions of any sort.

More to come!

 

[Darklefthand]

I was torn between lightweight and 'most stable/accurate' setup when I built my .308 gas gun. I did something similar to yours in that I piece-mealed it together from high end parts, but went heavy, since it was just meant to be a bench gun. Started with a Mega Maten MML reciever and handguard set. The premise being that since the handguard doesn't bolt to the barrel nut, but rather, to a shroud that protrudes from the upper, then there should be no deflection from loading up on the bipod. I also used a Bartlien stainless barrel. Man it's heavy, but shoots very tight groups. Very fun to shoot, as I'm sure your new set up is. Enjoy it!

 

[bigjake83]

Good looking rifle there ... Have you considered using the new buffer BCG's from JP that are specifically designed for running suppressed?? I only ask because they allow you to fine tune you're dwell time and that will shrink your groups even further when dialed in, also running JP SCS will soften the felt recoil even further due to the light weight nature of your build.

 

[MSTN]

Good looking rifle there ... Have you considered using the new buffer BCG's from JP that are specifically designed for running suppressed?? I only ask because they allow you to fine tune you're dwell time and that will shrink your groups even further when dialed in, also running JP SCS will soften the felt recoil even further due to the light weight nature of your build.

Those both sound like excellent ideas.

I saw the new JP VMOS bolt carrier at the SHOT Show. I should pick one up and try it.

The JP SCS has not worked out well for me at all in the past. But perhaps I should give it a second try.

At this point, I don't think I am capable of improving much on the results I'm getting. This rifle has shown a definite preference for Hornady 120 AMAX. Ill post some pix soon of the groups plus more of the complete rifle.

 

[bigjake83]

Those both sound like excellent ideas.

I saw the new JP VMOS bolt carrier at the SHOT Show. I should pick one up and try it.

The JP SCS has not worked out well for me at all in the past. But perhaps I should give it a second try.

At this point, I don't think I am capable of improving much on the results I'm getting. This rifle has shown a definite preference for Hornady 120 AMAX. Ill post some pix soon of the groups plus more of the complete rifle.

Sounds good ... and if you ever need any help on how to get all of those parts dialed in with each other to run harmoniously send me a PM I'll be more happy to help because once you get everything perfectly adjusted it make shooting a 308 AR just extremely easy and pleasant.

The JP SCS is a tool like any other and needs to be properly adjusted you can adjust your dwell time and your performance by taking out or putting in steel or tungsten weights inside the buffer system, you also have the adjustability of the spring rate. It does take some time two fiddle with it, but once you get it dialed in, boys is it lovely.

 

[MSTN]

The rifle seems to prefer Hornady 120 AMAX, so far. Too bad I only have three boxes of it! The top photo is of the first ten rounds fired with it at 100 yards. The following two photos are the last ten rounds from the first box fired at 300 yards.

 

[bigjake83]

Lookin good brother..

 

[samb300]

Nice rifle! I love the little details on lightweight components...the small machined scallops on each of the top picatinny rail sections are really awesome looking.

 

[MSTN]

Nice rifle! I love the little details on lightweight components...the small machined scallops on each of the top picatinny rail sections are really awesome looking.

Agree 100%. Whoever designs the components for 2A Armament apparently has absolutely no regard for what the CNC machine run time is to make this stuff. For example, look closely at the way the brass deflector is made. Not shown are numerous cuts made INSIDE the lower receiver to reduce every possible bit of weight. It is really overkill at its finest.

 

[jcsparky]

Wes, Any updates??
I know you working on SOMETHING.. !

 

[CSTactical]

That's a good looking setup!

 

[MSTN]

Wes, Any updates??
I know you working on SOMETHING.. !

I have a new bolt gun in the works which should be interesting:

Surgeon 591 action, small firing pin variant

KRG Habu chassis

PROOF Research 24" 6.5 CM carbon fiber wrapped barrel

It should be finished soon!

 

[dinmax82]

This is encouraging, I was hoping to do a 308 under 7lbs and I think I can easily get there.

 

[Strikerkc]

I've gotta say, this is really cool. One of the biggest issues I've run into that's kept me from having fun with long range gas guns, is that it's so easy to turn them into a real back breaker to lug around. Definitely saving this thread for later.