6.5 x 47 in Armalite AR-10 Gas Gun?

[Phil3]

I am building a bolt gun in 6.5 x 47 and at the same time, an AR-10(b) gas gun in the same caliber. I would like to use the 6.5 x 47 in the AR-10, but have some questions of those who have might have used this round in the AR. I am mostly concerned with brass life, the steep shoulder angle of the 6.5 x 47 feeding reliably (from Armalite AR-10b proprietary mags), firing pin function on small primers, and any issues with proper gassing using this round. I have other questions as well, so would appreciate hearing from those who have gone down this path.

Thanks.

Phil

 

[mac86951]

Feeding will be fine; small primer will be ok; however the bolts firing pin hole clearance is very sloppy for AR-10; look at a jp enterprises high pressure bolt and have your barrel + extension headspaced to that bolt (or checked).

Barrel length will be needed for gassing functions, an adjustable gas block is highly recommended to be easier on the brass. As is a "pad" on the brass deflector of the upper. I use a felt side of sticky Velcro and that seems to fit my budget and works great.

-Mac

 

[SG4247]

I have 2 AR-10s in 6.5x47. Works wonderfully, no problems in the Armalite large frame rifle.

 

[Phil3]

Hi Mac. Thanks for the quick reply. I looked at my Armalite bolt carrier group (Armalite part #10501001) and the clearance between the firing pin and the hole in the bolt face seems very small. I think the pin tip diameter is supposed to be 0.072". A 0.073" drill bit will not go into the firing pin hole, but a 0.070" bit will. I intend to send in my upper receiver and bolt for headspacing. I understand Krieger and Precision Firearms can set me up. Recommendations welcome. I was considering the JP Rifles adjustable gas block (is adjustable really needed?) and plan on an Armalite rifle length gas tube. Is there a desired gas port hole diameter? I will definitely use a pad of some sort on the upper receiver to protect the brass.

SG4247, your success gives me some confidence. How has the brass fared? Any tips you have on using a 6.5 x 47 in the AR-10 are welcomed. How has your brass fared? As an aside, parts I have now include:

Noveske N6 slower receiver (stripped).
Armalite lower parts kit.
Armalite buffer, buffer tube, spring (rifle).
Geiselle National Match Hi-Speed trigger.
Armalite magazines (metal AR-10b style, 10 and 20 round).
Armalite upper receiver (stripped).
Armalite bolt carrier group (BCG).
Armalite charging handle.
Armalite ejection port cover, hinge, spring.

All sourced around 2010.

Thanks.

Phil

 

[mac86951]

Excellent news on your bolt /firing pin size. The DPMS LR-308 models typically have a lot of slop.

The only reason I recommend an adjustable gas block is to allow you to dial down the gas to the point it will 'just' lock back on an empty mag. In theory this will be easier on the brass. In practice, it's a function of port pressure and dwell time of pressure. Port pressure is a big function of the load / ammo you shoot, and if you like slower powders say H4350, then may have higher port pressures. Alternatively, you can Taylor a load for your rifle without the adjustable gas block; all it provides is a larger window of performance.

If I was building my prone AR rifle again, I'd go 26" barrel and a rifle + 2" gas port. White Oak Armament has gas tubes for extended lengths.

JP is what I use for gas blocks. I like them and I've had no troubles.

Next truth is ARs are tough on brass. Gas system tuning helps, but bolt gun it's not. Brass catchers help, but somehow mine always dumps a hot case on my trigger finger.

I still get plenty of loads from my AR brass, and after tuning the gas system, I have a nice neat pile of brass about 8' away at about 4-o'clock. Super handy that several benches at our bench range just happen to have a concrete corner right in the path of the brass, but that's an easy problem to work around.

-Mac

 

[MikeMcCasland]

I'll add a huge plus to the +2 gas system recommendation; same with using faster powders. That in conjunction with a adjustable gas block will solve a lot of headaches.

'Tactical Brass Recovery' makes a brass catcher that works perfectly on my .260 AR10.

 

[Phil3]

I am not familiar with "+ 2" gas port terminology. Is this referencing moving the gas port in the barrel 2" further down the barrel than is normally the case (whatever that is). I know this all has to do with the proper gas pressure to the bolt carrier key, bolt unlocking, at the right time, etc., but do not know enough yet to make sure everything is correct for a 6.5 x 47 cartridge. I would likely use a 24" long barrel. If there is an article or something I could read on this, I would gladly read. In the mean time, perusing the Internet looking for some reputable trusted info on this.

I will check out the brass catcher. Thanks!

Phil

 

[MikeMcCasland]

I am not familiar with "+ 2" gas port terminology. Is this referencing moving the gas port in the barrel 2" further down the barrel than is normally the case (whatever that is). I know this all has to do with the proper gas pressure to the bolt carrier key, bolt unlocking, at the right time, etc., but do not know enough yet to make sure everything is correct for a 6.5 x 47 cartridge. I would likely use a 24" long barrel. If there is an article or something I could read on this, I would gladly read. In the mean time, perusing the Internet looking for some reputable trusted info on this.

I will check out the brass catcher. Thanks!

Phil

Yep. A "+2","Plus 2" or "Extended Length Gas System" (ELGS) is basically saying the same thing. With the larger 6.5 bore cartridges in the large frame ARs it really makes a huge difference in terms of port pressure and bolt unlock.

I've run a 20" rifle length gas system, and a 22" +2 gas system; both with adjustable gas blocks, and heavy buffers. The difference between the +2 gas system and standard was night and day. All other components being equal, I was getting pressure signs, and damaged case heads with the RLGS, using below starting charges of powder.

The extended length gas system alleviates quite a bit of those problems (at least it did for me). It had been trashing Lapua brass in 2-3 firings, but now you could probably get 6-7.

Edit: I can't speak for the Armalite versions as I built off the LR-308 platform, but it would be smart to grab extra bolt catches, or one of the expensive 'upgraded tool steel' versions. I broke a couple of the standard bolt catches before upgrading. That carrier is a monster, and a catch will break once you put enough rounds through it.

 

[mac86951]

I am not familiar with "+ 2" gas port terminology. Is this referencing moving the gas port in the barrel 2" further down the barrel than is normally the case (whatever that is). I know this all has to do with the proper gas pressure to the bolt carrier key, bolt unlocking, at the right time, etc., but do not know enough yet to make sure everything is correct for a 6.5 x 47 cartridge. I would likely use a 24" long barrel. If there is an article or something I could read on this, I would gladly read. In the mean time, perusing the Internet looking for some reputable trusted info on this.

I will check out the brass catcher. Thanks!

Phil

Yes the +2 terminology is black-rifle match terminology that specifies rifle length +2"; but also needs to distinguish between armalite and knights/dpms platforms as armalite rifle length isn't exactly that of DPMS. The trouble with the large format ARs; very much is platform specific unlike the AR-15 where everything meets one standard.
Trouble is that the large format AR is designed off of pressure curves developed with a 7.62x51 round and designed to always be reliable (read over gassed). To the effect of "It'll feed and cycle and who cares about brass."
6.5x47 and different powders make for different pressure curves.

I can say I built one for 7saum; and with rifle length gas port; and adjustable gas block; it functions.

-Mac

 

[mac86951]

Yep. A "+2","Plus 2" or "Extended Length Gas System" (ELGS) is basically saying the same thing. With the larger 6.5 bore cartridges in the large frame ARs it really makes a huge difference in terms of port pressure and bolt unlock.

I've run a 20" rifle length gas system, and a 22" +2 gas system; both with adjustable gas blocks, and heavy buffers. The difference between the +2 gas system and standard was night and day. All other components being equal, I was getting pressure signs, and damaged case heads with the RLGS, using below starting charges of powder.

The extended length gas system alleviates quite a bit of those problems (at least it did for me). It had been trashing Lapua brass in 2-3 firings, but now you could probably get 6-7.

Edit: I can't speak for the Armalite versions as I built off the LR-308 platform, but it would be smart to grab extra bolt catches, or one of the expensive 'upgraded tool steel' versions. I broke a couple of the standard bolt catches before upgrading. That carrier is a monster, and a catch will break once you put enough rounds through it.

And a few extra extractors too
-Mac

 

[mac86951]

Hey, I got a great suggestion for you Phil:
John Holinger at White Oak Precision knows just about everything AR, including large format. Give him a call, I believe they can also do all your machining too for what I would bet is a competitive price.

Another source of information is Carl at accuracy systems Inc in Byers CO.

I guess I'd like to say I'm knowledgeable, but first thing my AR taught me is that I don't know a thing. I'd hate to see you face the same dilemmas up front.

-Mac

 

[msalm]

I made a 6x47 Lapua on an AR10 platform and as mentioned use an Armalite bolt as the fp is smaller in diameter and if using the whole BCG you'll have the advantage of the firing pin spring keeping the firing pin rearward during cycling (slamfires).

The only issue I ran into with the 6mm version was Berger VLD's had too slender of a tip profile and wedged in the barrel extension between the lugs. Don't know if the same issue would exist with the 6.5's as I never tried VLD's in several 260's that I built.

 

[SG4247]

Same issue with the 6.5 Berger 140 VLD... thats the only 6.5 bullet that gives trouble in my 6.5x47 ARs.

I go 8 firings on -47 match brass - anneal at 5 times fired.

 

[Kurz]

There are no real secrets in this industry. We were doing this type of modification several years before Proof and others announced their findings. The .308's didn't create problems but the higher pressure cartridges, as pointed out, certainly raised their angry heads to let us know that we needed a control solution for the peak port pressure. Tuned port diameters, adjustable gas blocks and the longer gas tubes make all the difference in the world.

Here is Proof Research's version named Camgas:

With the release of its new patent-pending Caliber Matched Gas System (CAMGAS) barrels, PROOF Research has eliminated the issues traditionally associated with building 6.5mm and .260 rifles on 308AR/AR-10 platforms. Until now, AR-variant shooters looking for ballistic advantages from either of these calibers were faced with excessive bore pressures that necessitated makeshift solutions such as clipping buffer springs, adjusting buffer weights, and/or relying on adjustable gas blocks, to keep their rifles functioning properly.

PROOF’s R&D team has solved the overpressure issue with gas systems tuned specifically to the cartridge/barrel-length combination. “By moving the gas port, the pressure in the bore is given time to reduce to that comparable of a .308 Winchester with a rifle-length gas system, which is what the 308AR/AR-10 system was designed around,” said Greg Hamilton, PROOF’s research-and-development weapons specialist who’s also a 3-Gun and PRS competitive shooter. “The recoil impulse is noticeably smoother, which helps keep you on target while taking advantage of a more efficient projectile. Case extraction is also easier, with less case-head smearing, so the brass is in much better condition for reloading.”

In recent years, 6.5mm Creedmoor and .260 Remington have become increasingly popular in long-range shooting competitions. The .260 in particular represents an outstanding caliber for a military counter-sniper role—out to roughly 1,000 meters—in smaller- to mid-sized weapon systems. It offers exceptional accuracy and superior ballistics over the ubiquitous .308 while dishing out substantially less recoil and enough energy to make it a legitimate contender for military and law enforcement applications.

“I’ve been using prototype CAMGAS barrels, in both .260 and 6.5 Creedmoor, in competition for almost a year with excellent results,” Hamilton explained. “Both rifles ran flawlessly through high-round, fast-cadence stages, firing hundreds of rounds with 100 percent reliability and zero maintenance or cleaning. From recoil to reliability, every aspect of performance was improved compared to the typical un-tuned barrel.”

PROOF Research currently offers Caliber Matched Gas System barrels chambered for 6.5mm Creedmoor and .260 Remington in three separate lengths: 20, 22, and 24 inches. Every CAMGAS barrel comes standard with an easy to install custom-length gas tube.

 

[barefooter56]

I made a 6x47 Lapua on an AR10 platform and as mentioned use an Armalite bolt as the fp is smaller in diameter and if using the whole BCG you'll have the advantage of the firing pin spring keeping the firing pin rearward during cycling (slamfires).

The only issue I ran into with the 6mm version was Berger VLD's had too slender of a tip profile and wedged in the barrel extension between the lugs. Don't know if the same issue would exist with the 6.5's as I never tried VLD's in several 260's that I built.

The VLD bullet nose dimension is much longer than one for a bullet designed to be fed from a magazine. In a "single shot" mode after finding your bullet seating depth and velocity accuracy nodes its fine though. For magazine length ammo for the AR . Stick with our 6.5 130 AR/OTM or 6.5 135gr CLASSIC HUNTER bullets.

 

[mic2377]

While it is not a 6.5x47, I have a large frame AR in 6.5 Creedmoor. I built it several years ago before the current 6.5 Creedmoor craze, or prior to anyone besides DPMS chambering AR's in this caliber.

The gun has a 24" McGowen custom barrel, standard rifle-length gas. I use 10 and 20 round PMAGs. The bolt carrier group is a Fulton Armory small FP bolt, similar to the JP high-pressure and Armalite size FP. It does have an adjustable gas block, but it is opened fully as the gas port is properly sized.

While a +2 gas system is probably more "optimized," I have experienced ZERO issues with over gassing, damage to brass, or reliability. The primers look like they came out of a bolt gun, IE perfect. No issues with feeding either with the 6.5's shoulder angle.

Also a factor is that generally the lighter bullets are easier to get to shoot well, with better brass life, than heavier stuff out of gas guns. I run 123-130 grain bullets, with a velocity in the 2850-2900 fps range. After 3 firings, my brass still looks great. I think I will be able to get at least 7-8 firings easily, which is similar brass life to my 7.62x51 rifles.

I think you will be able to build a great rifle in any of the 6.5 cartridges, be it the Creedmoor, 6.5x47, or 260 Rem. Mine is amazingly capable for a gas gun built on the cheap and I have shot it out past 1100 yards with great results.

 

[Kurz]

While a +2 gas system is probably more "optimized," I have experienced ZERO issues with over gassing, damage to brass, or reliability. The primers look like they came out of a bolt gun, IE perfect. No issues with feeding either with the 6.5's shoulder angle.

There are exceptions to every rule and technical innovation. That's a fact just like opinions on the quality of rifle scopes and reloading components. Everyone has their own opinion based on their own experiences whether expert or amateur. I am passing along technical information which is proven by testing in the lab and by the general public. It is not an exception. If you choose not to accept this then you make that choice.

Enjoy your experience!