This guide covers the steps and torque specifications required for installing the AR-15 barrel. We'll also cover how to install the gas block and tube, allowing your barreled upper to function as soon as you install your BCG and throw it onto your lower receiver. Total installation time requires approximately 30 to 60 minutes. I'm important to have some specialty tools for this process, so let's see what's required.
Barrel Install: Grab These Tools
Vise (not pictured). A vise is required for securing the upper receiver while you torque the barrel.
Torque Wrench. A torque wrench is required to achieve the proper torque specifications for the barrel nut.
Breaker bar / Ratchet. You'll need to loosen and re-tighten the barrel nut three times. The torque wrench should never be used to loosen the barrel nut. Instead, use a breaker bar or ratchet wrench.
Barrel Nut Wrench. A barrel nut wrench will install on the torque wrench and lock onto the barrel nut to apply appropriate torque.
3/32", 5/32" Punches. Most gas blocks -- especially low-profile gas blocks -- use 3/32" and 5/32" roll pins for securing the block to the barrel, and the gas tube to the block. To seat these roll pins, punches are typically required.
Grease. To prevent damage to the receiver's threads and the barrel nut, grease is required when tightening and loosening the barrel nut. Simple Tetra Gun Grease or any other firearm grease is sufficient. Do not use grease that contains metallic additives like graphite or copper, as it will damage the receiver and weaken the threads over time. Military specifications say to use Aeroshell 33MS, though it's not necessary.
The Armorers Essentials Kit includes a torque wrench, Armorer's Wrench with barrel nut fitting, and vise block.
Receiver Vise Clamp / Reaction Rod (not pictured). The receiver itself can scratch or deform under high pressure when clamped in the vise. A receiver vise clamp or reaction rod (which seats on the barrel extension and clamps into the vise) is not required, but highly recommended to protect your receiver from damage.
Gunsmithing Hammer. To make seating the gas block and gas tube roll pins easier with punches, it's recommended you invest in a small brass gunsmithing hammer.
Allen Keys. Most gas block use a set of Allen-head holds to hold the block in place while you insert the roll pins. A set of Allen keys may be necessary for tightening these screws.
Gas Tube Alignment Tool. This helps to ensure the gas tube is aligned inside the upper receiver for interfacing with the gas key on the bolt carrier group during operation. You can simply install your bolt carrier and use it to align the tube if necessary.
Barrel Install: Parts Required
Barrel and Barrel Extension. Duh. Virtually all barrels come with the extension installed. We don't recommend trying to install the extension yourself. It requires an excessive amount of torque and industrial equipment is usually used.
Barrel Nut. The barrel nut secures the barrel to the receiver by clamping over the end of the barrel extension.
Gas Block and Tube. Make sure you have the appropriate gas tube for your barrel's gas system port length (pistol, carbine, mid-length, or rifle-length).
Gas Block and Tube Roll Pins. Make sure the gas block and tube roll pins are present.
Gas Block Set Screws. If your gas block uses Allen-head screws to secure to the barrel, ensure they're present.
Handguard and Handguard Nut. Your handguard may secure to your AR-15 using a nut that sits between the barrel nut and receiver. That means you might need to have your handguard and its hardware available for this install. We'll be illustrating this in this guide.
AR-15 Barrel Installation
First, make sure your receiver is safely clamped in your vise, preferably with a vise block or reaction rod.
Step 1: Insert Barrel Extension into Receiver
Apply grease to the barrel extension and receiver's threads. Then insert the barrel extension into the receiver and ensure the pin on the extension fully seats inside the notch in the threads.
Step 2: Hand-Thread Barrel Nut
Check your handguard's instructions to confirm whether you need to first install a fastener for the handguard before installing the barrel nut. If a handguard fastener is required, ensure it's oriented so the pass-through hole for the gas tube aligns with the gas tube hole in the receiver. Next, orient the barrel nut so the wrench fittings face the muzzle and hand-tighten the nut. You might need to remove the gas block if it came installed on the barrel with the set screws.
Once hand-threaded, check inside the receiver to confirm the feed ramps on the receiver and the extension perfectly align. If they aren't aligned, you may run into issues with ammo feeding from the magazine.
Step 3: Torque Barrel Nut Three Times
The barrel nut needs to be torqued, loosened, then re-torqued three times. This "seasons" the softer aluminum threads on the receiver and ensures the barrel is properly secured for accuracy and stability.
Barrel nut torque specs
Most barrels or handguards that use barrel nut fasteners come with advertised torque specifications. If your barrel or handguard does not provide torque specs, tighten the barrel nut to 40 to 50 ft-lbs. The U.S Army says an acceptable torque rating is between 30 and 80 ft-lbs. (page 3-43 of the mil-spec manual).
How to Properly Tighten and Loosen the Nut
Most barrel nut wrenches and adapters are open-ended. They can bend outward under torque, rendering them inoperable, if not used correctly. To properly tighten the barrel nut, seat the wrench so that the teeth of the wrench are pulled into the fittings on the nut. See below for the proper setup:
- Tighten the nut from the left side of the receiver, pulling the wrenches downward.
- Keep the barrel nut wrench and torque wrench parallel to each other to apply proper torque.
- Use the barrel nut with a ratchet wrench or large breaker bar. Do not the torque wrench to loosen.
- To loosen the nut, secure the barrel nut wrench underneath the barrel and pull up from the left side.
Repeat these steps three times, until tightening the barrel nut a final and third time. Again, torque to between 40 and 50 lb-ft. if torque specifications are not provided by your barrel or handguard manufacturer.
Step 4: Install Gas Tube and Gas Block
First, slide the gas tube into the gas block. Ensure the end of the gas tube with a small pin hole for the roll pin is inserted into the block.
Now slide the gas block onto the barrel, aligning the gas tube with the pass-through hole in the receiver, and handguard fastener if applicable.
Step 5: Install Gas Block Screws
Grab the roll pins and any set screws for securing the gas block to the barrel. Visually align the roll pin hole in the gas block with the notch in the barrel, and tighten the set screws. They do not need to be excessively torqued.
Step 6: Align Gas Tube, Install Gas Block Roll Pin
You can align the gas tube inside the receiver with an alignment tool or the bolt carrier Grab the larger roll pin and appropriate punch (usually 5/32") to install the pin into the block and barrel.
Tapping the roll pin into place can be difficult, as most gas blocks have rounded edges. It may help to reorient the upper receiver so the gas block roll pin hole is vertical. Gently tap the pin into place. You might try starting the pin with just the head of your hammer, followed by using the punch to fully seat the pin.
Most gas block pins are longer than the block itself. Ensure the pin is equally protruding from the block on both sides.
Step 7: Install Gas Tube Roll Pin
Now install the roll pin for the gas tube in the same fashion. It might help to have a pair of needle-nose pliers to hold the pin in the hole while you tape it into the block and tube. Like the gas block pin, tapping the pin directly with the hammer to get it started, followed by using a punch (usually 3/32") might work best.
Once seated, the gas tube roll pin should be flush on both sides of the block. Verify alignment of the tube is still correct inside the receiver with the alignment tool. If you left the bolt carrier inserted fully, alignment should be fine.
AR Barrel Install Complete
Your AR-15's new barrel and gas system installation is complete!
Now, you can refer to your handguard's instructions for securing the handguard or rail system to your rifle or pistol.