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So I built by AR-15 Pistol which was a fun build and has worked great until this weekend .... I tried to cycle the action and it would not return to battery. After looking at it I saw that the gas tube was pulled out of the gas block. I shook my head and put it aside until today. I have fired between 450-500 rounds through it without any malfunctions.

I don't think it is a quality issue with the parts. I used a Yankee Hill Low Profile Gas Block YHM-9383 and a Daniel Defense Carbine Length Gas Tube.

I took it apart and the gas tube was jammed into the gas key ... I got it out and it was a tight fit. Of course there was some carbon build up on it. The gas block looked fine, no wear or tear. The roll pin was just in the gas tube, well what was left of it. I grabbed a punch and got it out without any problems.

So I cleaned it up and noticed some burs on the end, got those cleaned up and put it back together. Then I searched the internet . . .

I read that since this is a free float handguard that you need to put a space in between the gas block and the barrel that is equal to the handguard thickness.

I don't know if this is right or not since I haven't seen anyone do this on the videos.

So the question in the end is do I need to put a space between the two? Any help would be appreciated. Thanks!
 

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If the gas block was designed to have the forend bracket behind it, you'll need to leave the allowance. If not, then you don't. If it's jamming the gas tube into the gas key and shearing off the gas tube roll pin, you have a problem, and need to address it - the gas tube doesn't have enough room between the block and the key when the bolt carrier group is closed into battery.

If the gas block WAS designed for a clamshell bracket, you'll be robbing yourself of gas flow to run it back against the barrel shoulder anyway.
 

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Discussion Starter #3
If the gas block WAS designed for a clamshell bracket, you'll be robbing yourself of gas flow to run it back against the barrel shoulder anyway.
That's what I am thinking the problem is .. I will take it back apart and put a space in there, I do have a handguard so I will use it to give me the gap that I need. It just gives me another reason to go to my happy place and tinker.

I am working on another one right now, it's going to be the rifle version with a fixed stock and baby even a "bigger" brother in 300 AAC Blackout ...

Thanks for the confirmation Varminterror!
 

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I confirmed it by loosing the gas block and spacing it then inserted my charging handle and BCG and then pushed the gas block back against the barrel. Clear as day you could hear it hitting the BCG. This gives me a lot of confidence that the problem is resolved.

I will be keeping my eye on it but it does seem to have fixed it for now based on my observation.
 

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So...

The next check. Oil an empty case, stick it in the chamber (or a rolled up cleaning patch), and blow into the muzzle while you slide the gas block back and forth. In the old position, seated against the barrel shoulder, the gas port will be partially obscured, whereas it'll feel more free flowing at the forward position.
 

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Thats new to me, not that it couldn't be possible. I have built 20 or 30, and never had to space the gasblock off the barrel shoulder for proper alignment. I usually after installing the gas block, and gas tube, I put a magpul polymer round in the chamber and use compressed air from the muzzle to make sure the gas block is properly aligned, the polymer bullet blocks the flow from the chamber, and allows the air to push with force from the gas tube, inside the receiver. By chance, did you install the gas block with the gas tube roll pin hole placed closer to the muzzle, I could see if you placed it closer to the receiver on the barrel, making the gas tube protrude further into the receiver. Just a thought. I have used yankee hill, midwest, and many other gas blocks, and never seen that issue before on mine, or others i have built, never had to space them, always tight against the barrels flange, unless i used a standard handguard like the a2 style or moe.
 

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I have had problems with a few builds where I did NOT leave the gap. While the hole in the gas block will be significantly larger than the hole in the barrel, they do need to be lined up properly.
 
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