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Posted: 1/18/2026 10:48:31 AM EDT
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I am assembling a 9mm upper. The upper has a gas tube hole, the barrel nut has a gas tube hole and the hand guard has a BLIND gas tube alignment port (10mm depth). Is there something I can semi-permanently put through there to help with keeping everything aligned? Yes, I understand that with enough (or the proper amount) torque, it should not spin off. I need the proper torque value, and then have all the holds line up for the upper hand guard to mate with the barrel nut. Having another anti rotation plug would be really nice. The upper hand guard does not have anti rotation tabs. |
Words fall from your mouth like shit from ass.
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On a 22 LR upper I used a piece of welding rod with red Loctite going through an A2 hand guard cap into the gas tube hole in the fixed A2 sight. I bought a CMMG 22 LR upper and they used a compression pin which is through the hand guard cap into the gas tube hole in the A2 front sight. Both have kept the hand guard and cap aligned for over fifteen years. |
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You can get compression pins commonly called roll pins at any hardware, auto parts or home supply store. Here is a link to the type of pin CMMG used. I don’t have the exact diameter of the gas tube or the hole in a gas block for the gas tube. The compression pin will squeeze down to fit in the gas block hole. The length of the compression pin doesn’t matter as long it is held solid in the gas block and has enough length to hold the hand guard cap. Any extra length will reside inside the hand guard. https://www.mcmaster.com/products/compression-pins/spring-pins-2~shaft-type~slotted/ Here is a picture of my CMMG upper where they used a compression pin in the gas tube hole through the hand guard cap. This might give you some ideas. 
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My 9mm barrel uses std front sight tower, A2 hand guards and barrel nut assembly Somebody sent ma a carbine gas tube that was popped from M16 use, and I cut the tube so it flush inside the upper (not stick out to interior of the upper) Pinned it to sight tower, and with aligned barrel to upper |
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I bought a set of split pins in SAE and metric, and no go. Went to the hardware store with calipers, no go as well. The split pins are not precision devices (duh), and either they are too big or too small. I am using a cut down nail at the moment and it is working, but does not keep it perfectly aligned (it does keep it from spinning off). I contacted the manufacturer, and the recommendation was to “torque away.” However I do not have a tool to properly apply that torque. Another option was to purchase a jig and modify the upper. That will be my final option, but it does seem to be the correct one. @amphibian Any recommendations? I was going to drop a line on your website, but thought this was better. |
Words fall from your mouth like shit from ass.
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Originally Posted By Steamedliver: @amphibian Any recommendations? I was going to drop a line on your website, but thought this was better. |
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Originally Posted By amphibian: Sorry, I don't really have anything to add to this discussion sounds like the other suggestions of using a cut off gas tube or the right size roll pin is what you need to to. Perfect. Thanks. |
Words fall from your mouth like shit from ass.
This may not be what you're looking for, but it's what I did when I built my 9mm about 20yrs ago. I used a cap screw with the head turned down to clear the upper handguard, and made a threaded cylinder that lightly press fit the inside of the upper receiver. The front sight has a 1" pin that goes in the gas tube hole, and is held in by the standard gas tube roll pin. (sorry no photo)
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