How To Install An AR15 Barrel

Aaron Spuler is a firearms enthusiast and recreational shooter. Follow more or his work at The Weapon Blog

Most DIY builders that routinely build or modify their AR15 have sufficient expertise to install or upgrade the barrel on their upper receiver at will. While it may be an easy task for them, a first-time builder will need to focus on some essential aspects when it comes time to attach the barrel regardless of whether it’s a modification, a repair replacement, or an upgrade.

You may also want to consider the type of AR15 barrel you pick. A heavier barrel will last longer than a lightweight one but the trade off is, of course, added weight. While most builders will choose a Mil-Spec barrel, another excellent choice that’s more durable is a barrel that’s been cold hammer forged. Be prepared to add another seventy-five to one hundred dollars to your build budget if you go the route of a cold hammer forged barrel.

Gas Tube Alignment-Check Tool.

As with any DIY project, having the right tools for the job will go a long way in reducing stress and ensuring a quality installation. Most builders overlook something you’ll want to make sure you have, and that’s a gas tube alignment-check tool.

This small tool fits into the carrier key of your bolt and becomes a critical part of the installation process. When it comes to the precise alignment of the gas tube, you’ll be glad to have this tool sitting on the workbench.

Receiver Block

For both removal and installation of an AR15 barrel, you’ll, of course, need a sturdy vice to hold the upper receiver in place. While you can accomplish the job by padding the vice tips to prevent marring or scratching the finish, you’ll probably want to invest in a receiver block.  

Place your upper receiver in the block by inserting the lugs into the block’s channel, then clamp the block itself firmly in place within the vice. Your receiver block will come with a set of pins that exactly match the size of your AR15 takedown and pivot pins and slip through the receiver and hold it in place.

A Torque Wrench a Breaker Bar and Properly Sized Head

As important as the gas tube alignment-check tool, you’ll need a wrench handle and an adequately sized head to break the existing barrel nut on the old barrel.

You’ll also need a torque wrench when installing the new barrel nut, but a word of caution here. Never use a torque wrench to remove or loosen a barrel nut. Doing so will damage the wrench and force a trip to the hardware store to purchase a new one.

For both the breaker bar and the torque wrench, a longer handle is advisable. When you need a little more nudge-power, you’ll be glad you got a longer handle wrench. Most heads these days won’t go around the nut entirely, but if you can find a 360-degree that fits securely around the scallops of the nut, you’re off to a great start.  

Even if you’re wrench head doesn’t go all the way around, make sure it’s properly secured and won’t slip before you begin adding pressure.

Don’t Forget the Anti-Seize

Before you slap that new barrel onto the receiver and start tightening the nut, you need to coat the nut’s threads and the receiver threads with liberal amounts of Anti-Seize.

Think about it for a second. Fastening the barrel to a receiver is a process of metal moving against metal. Without Anti-Seize, galling is sure to happen, and that’s a bad thing.  

Metal against metal under the simple friction of tightening the nut can create abrasive and damaging wear. When you factor in the pressure of twenty or thirty pounds of torque, the heat from the friction can weld the two pieces together. That’s not something you want to happen.

Installing That New Barrel

If you’ve come this far without mishap and have remembered to clean all the associated parts and apply a good coating of Anti-Seize, you’re ready to install your new barrel. First, slip the extension of your new barrel into the upper receiver.

You’ll know you’ve done that correctly because there’s a pin on the extension and a notch in the upper. The pin should line up with the notch. Let your torque wrench sit this one out for a moment because what you’re going to do is use a twist nut until it’s tight and then back nut securely and then back it off. You’ll need to do this at least three or four times.  

Here’s what you’re doing. Remember the Anti-Seize? You applied it to prevent galling when you tighten the nut down. Tightening the nut in this manner helps the surfaces of both the receiver and the barrel nut mate. The Anti-Seize prevents galling while your tightening and loosening is compressing the metal surfaces together. Don’t stop at two when four times will do.

Once the barrel is on, and the nut tightened, now’s the time for your torque wrench. Most barrels these days hover in the range of requiring thirty-five pounds of torque. However, this is just a minimum, and some barrel manufacturer’s minimum torque requirements may be higher. Usually, you’ll exceed the minimum torque in most barrel installations to achieve proper alignment of the gas tube.

Critical Performance

At the start, we mentioned an overlooked but essential tool known as a gas tube alignment-check tool. Some builders may tell you an AR15 can shoot without performing this critical step, and they’d be right. The thing is, you don’t just want to be able to fire your AR15; you want it to shoot as well as it can for as long as it can.

Here’s where it comes into play and how using it will ensure the quality performance of your AR15. Depending on the type of barrel nut required, it may be necessary for one of the scallops of the barrel nut to be centered in the gas tube receptacle in the upper receiver. Even more important is that the gas tube should not be making any contact with the nut. Proper tightening of the nut and performing a gas tube alignment check is a critical last step to your installation.  

Final Stage

Remove the bolt from your carrier group, insert your gas tube alignment-check tool into the carrier key then place the carrier back into the upper receiver. What you’ll want to see is a gap, even if it’s a small one, that rings the entirety of the gas tube tool. If you need to tighten or loosen the nut so that the tube tool doesn’t contact the nut anywhere, now’s the time to make that adjustment.

Finally, check to ensure the gas tube moves freely. You should give the upper a little shake and hear the gas tube rattle a bit. If you can hear it rattle, it means the tube is free-floating and can operate with no constricted movement.