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99% of your Budget AR problems, explained in one article.
- Thread starter mtdawg169
- Start date
Absolutely the best post of the year on ODT. Agreed completely.Another subject the article touched on is the misaligned gas tube. I have witnessed misaligned gas tubes is a few factory guns (one of the worst was a Colt M4) and just about every home built AR I have ever seen. A misalignment in a gas tube can be so slight it's almost imperceptible, or so far out of spec it makes charging the rifle a real feat of strength (like the aforementioned Colt M4). Whether slight or far, gas tube misalignment will lead to accelerated gas tube wear at the gas tube/carrier key interface.
Way out of spec gas tube:
View attachment 1083458
Aligned gas tube:
View attachment 1083459
While poor gas block alignment can contribute to gas tub misalignment, more common (at least from my perspective) the culprit is an improperly indexed barrel nut. Installing the barrel nut requires two distinct steps, proper torqueing AND indexing of the nut. The barrel nut torque range on a standard AR runs from a minimum of 30 ft/lbs to a max of 80 ft/lbs. So once the barrel nut is properly torqued within that range, the nut is aligned by tightening the nut as required to align it with the opening in the upper receiver for the gas tube to pass through. There is a tool used, a "Gas Tube Alignment Gauge Pin", to check alignment. In a pinch I have used a drill bit to do the same check.
Checking tube alignment during barrel nut install/torqueing using a Alignment Gauge Pin:
View attachment 1083464
Once your are satisfied you have the barrel nut aligned properly, there is on final check to insure you are good to go. Install the gas tube, then take your bolt carrier only (no bolt/cam pin/firing pin/ firing pin retaining pin installed) and insert it into the upper receiver. Make sure the charging handle is not installed while you conduct this final check. Slowly push the bolt carrier forward until it seats firmly against the barrel extension, just like it does when the bolt carrier group is in battery. As you do this the gas tube will insert into the carrier key. If the barrel nut is indexed properly, resulting in proper gas tube alignment....you will feel little to no resistance as you push the bolt carrier into the in battery position. If you feel resistance? Then time to remove the gas tube and realign the barrel nut. I have seen some recommend using a big flat head screwdriver to bend the portion of the gas tube that is visible in the upper receiver into alignment as an easy fix. While that may turn a badly misaligned gas tube into a slightly misaligned gas tube, I prefer an in-spec rifle.
One last note. No matter how perfectly aligned the gas tube, like many other parts in an AR (I have witnessed Bolts, Firing Pins, Extractors, Disconnectors, Springs, and on and on go south) it eventually wears out. This is a picture of a gas tube I recently replaced in a Colt M4....the type with a giggle switch. The carbine had somewhere between 15,000 to 20,000 rounds through it. The end user brought to me to diagnose an intermittent feeding issue. His story was "sometimes, but not always I will pull the trigger and the weapon will not fire. I will conduct a failure to fire drill and it runs fine. I have noticed that when it happens the gun is hot and the chamber is empty when I rack the charging handle." The first thing I did is ask....."ARE YOUR GAS RINGS STAGGERED!" I kid, I kid. The first thing I actually did was check the carrier key. Here is the business end of the gas tube:
View attachment 1083499
Completely smooth all the way around! 10 minutes and a new gas tube later.....100% reliable again.
The moral of the story? I guess it's there is a lot more that goes into to building a reliable AR than putting parts together. And even more importantly, a slightly out of spec AR can run reliably for a long time.... when reliability is measured by shooting a few hundred rounds a year. But without, a doubt a well built in-spec AR will outperform and outlast a slightly out of spec AR every time, and run farther - harder - faster while it's doing it. As always, YMMV.
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. And holy worn gas tubes, batman! Wow.
Here is a pic of a Colt proof tested and magnetic particle inspected "MPC" bolt that eventually failed. I don't know the round count on the bolt. It came out of a Colt R0933 (Colt 11.5 inch Commando) I was doing a barrel replacement on for an officer from another agency. The gun was running fine, but was key holing rounds lake crazy. Obviously this bolt was well on it's way to perdition.
I know.....But I couldn't bear to do it! Not when aligning the barrel nut/gas tube in really a simple exercise.CQB27 What's crazy is that the TM actually demonstrates using the "bend it to fit" method of gas tube alignment.
![](https://www.theoutdoorstrader.com/javascript:editorInsertAtCursor( '<img src="/images/smilies/smiley_abused.gif" class="sm">', '[BD]' );)
I know, right?I know.....But I couldn't bear to do it! Not when aligning the barrel nut/gas tube in really a simple exercise.
