Lead on an AR-308 accuracy problem. Gas tube misalignment.

arlaunch

arlaunch

Active member
I have put together so many AR's complacency got me.

After going through a Criterion barrel, then upgrading to a Krieger barrel i still can't get the rifle to shoot.

Today i pulled the bolt out of the carrier and ran the carrier back and forth. I found out it was a bit sticky/binding. I ended up cleaning out the carrier key and that helped a bit.

The cause of the binding was not the gas block being misaligned, but the receiver inlet and/or the barrel nut not lifting the tube high enough.

Primer boxes have a thicker paper material. I used that as a shim and stuck it under the gas tube at the part where the hand-guard slides on.

With that shim..... The bolt goes back and forth like there is no gas tube there. Like it does on all my other rifles.

I would like to put devcon epoxy on the upper receiver gas tube inlet. Seems most epoxies i have on hand are rated for around 250-300° F.

How hot do you think the upper receiver gets right there where the gas tube goes in?
Other suggestions?

The only other thing i can think of is adding a weld on the barrel nut, then filing it back down.

I suppose i could try bending it. I am worried i will tweak it though.

 
I would definitely bend it to make it work, actually you want it going through the barrel nut without touching anything if possible. I've gone to great lengths and lots of painstaking effort installing gas tubes and getting it to where it doesn't touch, and the bcg doesn't deflect it more than the bare minimum amount. I would definitely not add any material anywhere to deflect it into place.
 
It's a cheap tool made for industry. Seems brake lines and such.

Not sure if it will work. Will post results. Seems it arrives tomorrow at some point.

I have spent many a days fretting over poor accuracy after spending by far, more than i have ever spent on any other rifle.

If this comes together i will be one happy camper.

In the mean time i have many times considered the merits of the large platform rifle. Its far from my preferred choice for a Coyote rifle. It has no where near the punch of my 270 Win or 7mm Rem mag. It is very heavy and not comfortable at all to pack around.

At least if it starts to shoot well it will have that???
 
It should have some impact, I don't know if it's a miracle cure though.

Yeah the large frames can be tanks. I have one in 300 Saum and it's plenty accurate but it doesn't see much daylight, for several reasons including the fact I don't have a lot of use for the more powerful calibers other than longer range target shooting.

If I wanted a 308 now I'd start with that new ruger sfar which is ar15 sized. My 243s are a medium frame which are closer to ar15 size than large frame size.They carry nice and are very accurate.
 
This rifle does not shoot terrible, yet it does not shoot well either. I can.... from time to time get .9's and 1.1's. It is not repeatable always though. Many groups are ruined by a high flier. Straight up from the group and inch or so.

The bender arrives today Amazon says.

I also have pulled the muzzle device and will try to shoot groups w/o that.

It has a Y/M chrome carrier, JP bolt head spaced to the that barrel and a Krieger gas block. Just about the finest components i could buy.

Seems if the low profile gas block had the tube raised a hair i would not be having this problem?
 
As i get deeper into this project the problem may be just component fitting. Seems no matter which way you bend the gas tube, it still goes into the receiver loaded upwards on the barrel nut, and then continued tension into the gas-tube/receiver slot.

I bent the tube a few times. (tool not really used that much/wondering if i needed it at all) Now there is no binding or even drag as the carrier slides back and forth with the bolt removed.

To remedy the the tension/loaded gas tube i took a saw chain file and filed out and down the round slot the tube goes through on the barrel nut. I also took a flat file and did some minor filing on the barrel nut to relieve tension.

Seems before the gas tube tension was loading the the gas block. That coupled with carrier key binding....

Will see how it shoots when i get the chance to take it out. Unfortunately with no control group.... It is somewhat a crap shoot. I do have a lead though... 39-41 grains of H4895 and BR2 primer with a Sierra 168gr.

Will try a few 5 shot groups in there.
 
I understand your frustration. When I got my 6.5 Creedmoor AR I started with 140 grain hotter load I would shoot in a bolt action. It wasn't good. I dropped to 95 grain V max with a milder powder charge and it was a half MOA gun. If I wrap my hand around the grip on my 308 it will throw a flyer. The only way I can get rid of that is only put center pressure on the front of the grip. Some of the headaches I went through.
 
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