Gunsmithing How To?? AR gas block install question...

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Sgt_Jamez

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Dec 24, 2009
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Carmichael, CA
#1
I have installed gas blocks on ARs before, but my rifle is suddenly short-stroking (doesn't lock back on last round, occasionally doesn't pick up next round from the mag) after changing over to a Troy low-profile GB.

What method do you guys use to line these up? I tried taking a ruler and penciling a line through the center of the gas port on the barrel and then doing the same on the gas block. Maybe I need better alignment of my pencil line?

Also I did apply blue Loctite to the barrel band and also on the gas tube itself. If I goobered up the gas port w Loctite wouldn't there be enough pressure to blow that loose? Is this an alignment issue or Loctite induced?

Are there any pictorial walk throughs? I am feeling kinda dumb here so if someone can break this down Crayola-style for me, I would appreciate it. Thanks!
 
#2
Re: How To?? AR gas block install question...

Really the alignment part is simple. I'm thinking that you have most likely "goobered" up the hole or the tube itself. It sounds to me that you simply are not getting enough gas blowback through the tube to completely cycle the bolt. One thing to keep in mind is that when loctite sets up, it gets really hard and if there is a big enough piece or multiple pieces, then it could very likely either block completely or partially (which is what I believe you are experiencing) the tube/tube hole. I would recommend that you take it back apart...if you can get it apart and clean/double check things. I'm betting it's not your barrel hole alignment, as your procedure you outlined should be plenty accurate enough, but it's the loctite that's causing you the problem. Just FYI, I'm limited in my AR building experience, with only having done a handful, but I've never had to use anything on the tube/block to make a rifle function properly. Put the tube in and pin it, then line up the gas block and secure it. If it's a pin on version, you really can't get those off too much. A clamp on, which I'll bet is what you're dealing with is alittle different story.
 
#3
Re: How To?? AR gas block install question...

I've done 6 or 7 of these and thought I had it dialed. Guess not. I've used Loctite before and never ran into this. I just thought that with the 50K+ psi at the gas port that a little loctite would be blown through. I'll heat up the GB and take it all apart and put it together with no loctite and see what happens. The only reason I used any "bedding" was that the last GB had leaked large carbon deposits onto the barrel at both ends.
 
#4
Re: How To?? AR gas block install question...

What kind of gas block are you using (pinned, clamp on, set screw, flat top, etc)?

This might sound ridiculous, but I have always just eyeballed mine. To test it, plug the chamber and blast/blow some air through the muzzle and you should feel it coming out the gas tube. I have never used LocTite on my gas blocks; to me that is indication of a poor fitting block.
 
#5
Re: How To?? AR gas block install question...

It's a Troy low-profile set screw type block on a 16" barrel w carbine gas port and a Troy TRX handguard over it.

This is the first one that I have ever had issues with. Just wondered where I went wrong.

It is my understanding that there is too much pressure in the gas tube for it to get blocked. Is this an incorrect statement?
 
#6
Re: How To?? AR gas block install question...

too much pressure? I can't attest to whether it will blow out a blockage or not. I would speculate that alot of that question will determine exactly what the debris is that is blocking the tube. Carbon will build up in the gas tube and cause malfunctions, so my guess is that it is not guaranteed that anything will be blown out.
 
#7
Re: How To?? AR gas block install question...

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: TacticalJ</div><div class="ubbcode-body">too much pressure? I can't attest to whether it will blow out a blockage or not. I would speculate that alot of that question will determine exactly what the debris is that is blocking the tube. Carbon will build up in the gas tube and cause malfunctions, so my guess is that it is not guaranteed that anything will be blown out. </div></div>
I am sorry but I have shot ARs for years and thousands of rounds down the tubes with no sign of carbon build up in the tube before. Where did you get this information from?
 
#10
Re: How To?? AR gas block install question...

It is possible to get small amounts of build up. It depends on if you are useing cheap wolf ammo and alot of it. I have the troy low pro gas block on three rifles and have had no issues. Have you tried cleaning the gas block and tube? I would soke them both in acitone for a couple minutes and then clean them real good. If you have a air compressor you could try blowing them out. Good luck.
 
#11
Re: How To?? AR gas block install question...

This...

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: BigBlue&Goldie</div><div class="ubbcode-body">I would guess the block is either crooked, or the gas port is drilled too close/far from the shoulder that the block rests against on the barrel. Take it off and measure those distances with your caliper. </div></div>

Locktite ain't gonnna block the hole, there's 12-20,000 psi pressure there. Also, locktite only hardens in the ABSENCE of air (it's an ANaerobic adhesive, as opposed to AIRobic), so it will not fill up a hole.

When you remove the block, look at the hole in the barrel and block, you'll see where the hole is misaligned by the carbon ring around the holes.

Probably too far forward or back.
 
#12
Re: How To?? AR gas block install question...

I agree that there must be a misalignment. I measured the distance from the shoulder to the center of the gas port and came up with .300". The edge of the gas block to the center of the hole was .289". When I mounted the GB, I butted it up to a .010" feeler. I am guessing I drew my center lines wrong and the alignment error is not front to back off the shoulder as it is the rotational alignment around the barrel.
 
#13
Re: How To?? AR gas block install question...

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: RWH82</div><div class="ubbcode-body">It is possible to get small amounts of build up. It depends on if you are useing cheap wolf ammo and alot of it. I have the troy low pro gas block on three rifles and have had no issues. Have you tried cleaning the gas block and tube? I would soke them both in acitone for a couple minutes and then clean them real good. If you have a air compressor you could try blowing them out. Good luck. </div></div>
I would have to see it. I have shot wolf also and no issue. Tested it the yesterday with a tube cleaner and it came up the same with all loads, clean.
 
#14
Re: How To?? AR gas block install question...

I have seen it in the M16's and some M4's but it was not very bad. Thats why we were issued "tube cleaners". I figured it was the ammo he was useing, in the army guys would never clean there wepons and it would build up.
 
#15
Re: How To?? AR gas block install question...

Apply some compressed air from the action side, may give you a idea whats going on.

I had a block that was was not drilled all the way through. It was enough to randomly unlock the bolt.

Compressed air should flow right through without restriction
 
#16
Re: How To?? AR gas block install question...

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: RWH82</div><div class="ubbcode-body">I have seen it in the M16's and some M4's but it was not very bad. Thats why we were issued "tube cleaners". I figured it was the ammo he was useing, in the army guys would never clean there wepons and it would build up. </div></div>
My point was I have shot over 5000 rounds in that gun without cleaning more than the bolt and the barrel once. The gas tube was still clean.
 
#18
Re: How To?? AR gas block install question...

So there is no step by step tutorial with pics on how to correctly index a set-screw gas block? I am a visual lerner and it helps me a lot to see people's processes. I think I am on the right track, but just messed up somewhere.
 
#19
Re: How To?? AR gas block install question...

Ok for the troy low pro gas block. I marked center of the gas port coming out of the barrel once I have center I transfer the line to the edge of the back where the gas block butts up with the barrel. I use a small chisle and mark the line double checking every thing. Then on the inside top of the gas block where the gas port is drilled I do the same. When doing these steps take your time and messure twice. By doing it this way you will have perffect alinement, just line up your two small marks made by your chisle. As for setting the screws each will be differnt but I set the block with the rear screw first and once it alined I mark the front by putting wet nail polish on the tip of the screw. Insert the screw slowly then take it out. Remove the rear screw and take the gas block off. Use a small drill bit or a drimel tool and put a detent where the nail polish is. Reinstall the gas block make sure it alines then do the rear. Once you finish this process use lock tight on your screws. If you do it this way test fire the rifle to make sure it works then do the last step.
 
#20
Re: How To?? AR gas block install question...

The last step is to mark three punch marks around each screw this will insure that the gas block screws will not back off. This is how I have done it for the last twenty rifles or so. I have had no problems as of yet. Be mindful that I have done this alot so it seams farley simple to me. If you dont fell confudent in doing it this way seek alternate advise. If you need more help Ill see if I can get some pics up of the next one I do. This method will work for other blocks to.
 
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