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Old 11-15-2012, 15:31   #1
Walt_NC
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How to ensure proper gas block alignment?

Out of curiosity, how do you guys go about ensuring that you have proper gas block alignment with the barrel port on barrels that aren't slotted or drilled for pinned gas blocks?

Most guys I know just eye ball it and then shoot to confirm that everything is working. I understand that the port on the gas block is larger than that of the barrel so there is some wiggle room. Still, that method has always bugged me as I think a partially obstructed gas port could result in pressure-related reliability issues.

My method:
I seal the muzzle-end of the barrel by wrapping 100 mph tape around the barrel extension. Then I will use a compressor to run about 40 PSI of air through the gas tube as I slide the gas block back and forth. I listen to the air flowing out of the muzzle and then tighten the gas block screws when it sounds like I'm getting the largest volume of air from the muzzle. I will then remove the gas block and lightly dimple the areas where the set screws have scored the underside of the barrel.

Is there a better way of doing this?
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Old 11-15-2012, 17:11   #2
Travclem
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I just put a pencil mark down the top of the barrel from the port and another one on the center of the gasblock and line them up. I have yet to have one not line up (out of 17 rifles).
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Old 11-15-2012, 17:50   #3
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Quote:
Originally Posted by Travclem View Post
I just put a pencil mark down the top of the barrel from the port and another one on the center of the gasblock and line them up. I have yet to have one not line up (out of 17 rifles).
That's exactly what I do too. When I first learned how to assemble an AR the guy that showed me how to do it did it so I just carried on doing it....
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Old 11-15-2012, 18:34   #4
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I measure and mark...
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Old 11-15-2012, 18:44   #5
Cole125
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Take it to a competent gun smith and have the gas block pinned, of course he will also perfectly align it for you.
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Old 11-15-2012, 19:47   #6
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I have all mine pinned. But its not hard to align it properly if you are intent on using the set screws. The thing you need to understand is the gas port is drilled right through the same hole that holds a set screw. So if you rotate the gas block so its upside down with the set screw hole facing up--you can then visually center the set screw hole over the gas port in the barrel. Hell--drop a drill bit in the gas port hole if it helps you. Then carefully scribe lines on the top and bottom of the barrel and gas block and then simply rotate the gas block 180 degrees until your lines match up and it should be perfectly aligned. There is a fair amount of tolerance built in there and if your are off by a few thousandths either way its no biggie. Mark your set screw holes on the bottom. Remove the gas block and center punch your set screw locations and drill some index points for the set screws. Assemble using red loctite. Leave it alone for a day to set. Go shoot.
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Old 11-15-2012, 20:18   #7
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Quote:
Originally Posted by Cole125 View Post
Take it to a competent gun smith and have the gas block pinned, of course he will also perfectly align it for you.
I don't pin mine. They are all low pros under the rail. I only have one pinned GB and it is a shaved FSP. Have you ever had a problem with one that wasn't pinned?



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Old 11-15-2012, 20:18   #8
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Quote:
Originally Posted by Cole125 View Post
Take it to a competent gun smith and have the gas block pinned, of course he will also perfectly align it for you.
OP's way of doing it will work just fine.
While pinned is the MOST secure, if the barrel is dimpled & the set screws
have thread locker applied, the gas block will be just fine. This, as well as the
rail covering the gas block, not a chance of it working loose.

Last edited by faawrenchbndr; 11-15-2012 at 20:19..
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Old 11-15-2012, 21:04   #9
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Quote:
Originally Posted by Travclem View Post
Have you ever had a problem with one that wasn't pinned?
Yep I had a Troy low pro gas block move on me and the rifle started short stroking. I learned my lesson and now only run pinned gas blocks.

Its well worth the cost and slight hassle of taking your gun to a gun smith, or you can send your upper to ADCO.
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Old 11-15-2012, 21:27   #10
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I like to make markings of the center line of the barrel gas hole and the outside diameter of the hole with an pencil on the barrel and gas block. And then I use one of these bad boys. It's a Daniel Defense low profile clamp on gas block. Fits under every rail and holds very well on the barrel.

Black Rifle Forum

But before I tighten everything, I make sure that the barrel nut is perfectly aligned, and than I make sure that the gas tube rides perfectly into the gas key. I hate clicks and bindings there. Sometimes tiny (few hundreds of a millimeter) gas block twist adjustments are necessary to get that gas tube/gas key alignment perfection. The gas hole in the gas block is bigger than the hole in the barrel, this allows an small amount of gas block offset. Thats why like to make markings of the outside diameters on the barrel and gas block.


This is one of my favorite tools. It's a gas tube/barrel nut alignment tool. Makes it a lot easier and better.

Black Rifle Forum

Last edited by Made in Austria; 11-15-2012 at 21:43..
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Old 11-15-2012, 21:47   #11
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Quote:
Originally Posted by Cole125 View Post
Yep I had a Troy low pro gas block move on me and the rifle started short stroking. I learned my lesson and now only run pinned gas blocks.

Its well worth the cost and slight hassle of taking your gun to a gun smith, or you can send your upper to ADCO.
Exposed or under a rail? I could pin it myself, I've just never messed with it because I've never had an issue.
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Old 11-16-2012, 05:06   #12
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The only way a gas block will move is due to improper installation.
If you dimple & use thread locker,....you are good to go. Have a upper
with 7400+ rounds, gas block has never shifted or loosened.
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Old 11-16-2012, 05:30   #13
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Quote:
Originally Posted by Travclem View Post
I just put a pencil mark down the top of the barrel from the port and another one on the center of the gasblock and line them up. I have yet to have one not line up (out of 17 rifles).
This is the way I do it.

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Old 11-16-2012, 07:37   #14
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Quote:
Originally Posted by faawrenchbndr View Post
The only way a gas block will move is due to improper installation.
If you dimple & use thread locker,....you are good to go. Have a upper
with 7400+ rounds, gas block has never shifted or loosened.
I have several rifles with DD clamp on(gasp) gas blocks and one with a YHM set screw gas block. All under DD rails and have never had an Issue. My hog rifle has ~11k through it and I have others creeping up on 10k and not one gas block issue. I was just curious as to what caused Cole's to loosen up.
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Old 11-16-2012, 10:10   #15
Walt_NC
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Hey guys. Thanks for the responses. I think I will continue to do it the way I have been but will also use the pencil marks as a redundancy. Thanks again.

Oh, and I forget who asked but with a low pro gas block using set screws (as opposed to the clamp on style), a dimpled barrel and Rocksett thread locker, I have never once had a gas block move on me.
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Old 11-16-2012, 10:32   #16
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Have never used a clamp on, except a dedicated .22lr upper.
May try one on a future build
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Old 11-16-2012, 10:58   #17
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Have you seen this test that MM did with the VLTOR clamp on?
http://www.militarymorons.com/weapons/ar.optics2.html

2/3 down the page. Pretty impressive, @100ft/lbs of torque on the gas block the barrel indexing pin sheared and the GB didn't move.

I've never used the VLTOR, nut I have not had any issues with the Daniel Defense clamp on low pro blocks.
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Old 11-16-2012, 22:47   #18
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Quote:
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Exposed or under a rail? I could pin it myself, I've just never messed with it because I've never had an issue.
The gas block was under a FF rail. Again it pays to spend a little money and get it pinned.
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Old 11-17-2012, 05:17   #19
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Quote:
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The gas block was under a FF rail. Again it pays to spend a little money and get it pinned.
Good to know. No doubt that pinned is better, I just never have messed with it.


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