AR15 Barrel/gas tube length

[allen529]

I have asked this in several different boards but no one has responded.

Is there a barrel/gas tube length that would allow an AR to shoot at 24' bolt gun velocities safely? Specifically an 80 gr Berger VLD through a polygonal 7 or 8 twist barrel.

Thanks

 

[effendude]

Allen, I suggest you contact John Holliger at White Oak Arms in Ill. He is an awesome AR guy and should be able to help. Don't be disappointed if you get an answer you don't want...AR's are not bolt guns...Good Luck, Scott

 

[allen529]

Scott,

Thanks for the reply. WOP is the inspiration for my madness here.lol I see that they have 26' match barrels,AR) with a gas tube 2' past rifle length and I was curious as to how much more or less velocity they were making compared to a 24' bolt gun.

I figured it was not possible to get true bolt velocities but had to ask the question to make sure. lol

I am probably going to go with a palma length heavy AR match barrel for my gas gun and if its accurate enough shoot midrange F-class. Just depends kinda thing floating around in my pea brain.

Allen

 

[effendude]

Allen,
I have a couple WOA 26' tubes. Great barrels, good value. I don't have any from the Precision side of John's operation yet. I'm no expert, but the longer gas tube is a must and I'd suggest Tubb's Superior Shooting Systems Carrier Weight also. The CWS does make a difference with hotter loads. Have John make your barrel, you'll be happy. I don't have any chrono data, but accuracy for F-Class is very good.
Scott

 

[kevinbritvec]

The gas port has been moved forward because everyone is using slower powders and heavier bullets causing increased port pressure at the old location. This times the action unlocking closer to the original specs. If you run too long and too heavy a barrel you risk stressing the upper receiver. I don't think you'll gain much velocity past 26' for all the unweildly weight you'll gain. I've gone to .812' diameter in front of the gas block when running these barrels and .875 under the hand guard. Accuracy is still great and I can pick the darn thing up now.

 

[allen529]

Kevin & Scott

I honestly was thinking about 1' under the free float tube and .935 at the gas block all the way out. The longest barrel I really considered is 28' with WOA's 15.3 length gas tube.

This is nothing more than a prone gun shooting from a bipod out to 600 yrd with a rare shot out to 1k.

You did raise another interesting point. Powder selections. I have Berger 80 grn in mind for the midrange and even 1k but then I would have to work up a load or two carefully.

Allen

 

[ronemus]

I've had the best results for 75 gr bullets,Hornady BTHP and A-Max) using N-550. RL-15 can make the same velocity, but pressures are higher and barrels wear faster. I think RL-17 will be great and I have test rounds loaded,75 gr A-Max and BTHP, Berger 90 gr), but I haven't had decent weather to go to the range.

I second WOP barrels - I have John do all of mine; his work is superb. My 28' spacegun barrels are 1' under the handguards, 0.935' at the gas block, and 0.920' to the muzzle. The velocity gain vs. a 24' is small, but I like the balance and increased sight radius. Even with a 24' barrel, my brass took a beating,rim lifts) with the gas port at the standard rifle location. Moving the port forward 2' cured that on 24-28' barrels.

 

[allen529]

Thanks, ronemus for the info.

 

[AP2020]

I have resurrected this thread because of my current AR 15 Build...

....6.5mmBR, 26" Pac-Nor Barrel, 1:8.5 RH Twist

Guys had referenced moving the port forward 2" cured that on 24-28" barrels.

As I am new to AR 15 builds, I wonder what that dimension is = 2" past?, and where can I find the longer gas tube?

thank you!

 

[livelyxp100]

Plus 2" gas tubes are available from 6mmar.com ar-x enterprises. I just ordered some for my 20 br build Paul

 

[Matt Pitchon]

I shoot a 26" 7.7 twist Kreiger with the gas port at the standard location. I am shooting 90HPBT at about 2770fps for the 600. This is a hot load. The brass was showing heavy extractor (not ejector) marks, near ripping the rim off. I tried an adjustable gas block which helped, but did not eliminate the problem. Then I replaced the gas rings and gas tube, and amazingly the problem went away. I still can't figure out why this changed worked. I would have thought better gas sealing would make the problem worse. I can only speculate that the bolt unlocked earlier, before a build up of pressure forcing the bolt open. With worn gas rings, the bolt would stay locked while pressure built up then forcing the bolt back violently. Once again, I can only speculate. This result is not what I expected, but it is clear that the rims are no longer damaged.