Upper Receiver Assembly (AR-9, AR-15, and AR-10/LR108)
Step U4: Barrel Installation
Objective: In Step U4 of upper receiver assembly, we will install the barrel.
Tools Required
1: Breaker bar required if removing an existing barrel nut. We also recommend exercising the barrel nut (Step U4-5) with a breaker bar.
2: Included with Aero Precision Enhanced upper receivers.
3: Select appropriate wrench for your barrel nut.
4: Not required for Aero Precision Enhanced upper receivers. Only required for threaded uppers. You could also use your gas tube (be careful not to damage it) or a #15 drill bit.
Components Required
| Quantity | Component |
|---|---|
| 1 | Upper Receiver |
| 1 | Barrel Nut1 |
| 1 | Barrel |
1: Included with Aero Precision Enhanced upper receivers. If using a threaded upper, the barrel nut may be included with (or purchased with) the selected handguard.
Instructions:
Step U4.0: Remove Existing Barrel (replacement/upgrade only)
If you are replacing your barrel (or need to remove your barrel for any other reason), first ensure the firearm is unloaded.
You will need to remove the handguard before you can remove the barrel.
If you are replacing the barrel and will be reusing the gas system and/or muzzle device, you will need to remove the muzzle device and remove the gas system, as applicable.
Using the appropriate barrel nut wrench and a breaker bar (DO NOT use a torque wrench to loosen!), loosen and remove the existing barrel nut. Remove the existing barrel. Wipe the barrel extension pocket of the upper receiver and inspect for debris or obstructions.
Step U4.1: Lubricate the Barrel Extension
Wipe a thin layer of high temp grease on the barrel extension. Not many people make this recommendation. We do this to 1) make installation easier (you get better seating of the barrel extension into the receiver), 2) to prevent galling and corrosion where the steel receiver extension meets the aluminum upper receiver, and 3) to make barrel removal easier in the future.
Step U4.2: Install the Barrel into the Upper Receiver
If applicable, remove the barrel nut from the upper receiver.
With your upper receiver mounted on an action rod and vice, insert the barrel extension into the upper receiver. Ensure the indexing/alignment pin on the barrel extension seats into the recess in the top of the barrel extension pocket in the upper receiver.
Step U4.3: Grease the Threads
WARNING: DO NOT USE THREADLOCKER
Apply a light coat of grease to the male threads of the barrel nut (Aero Precision Enhanced upper) or upper receiver (all other uppers).
Step U4.4: Install the Barrel Nut
Slide the barrel nut over the barrel until it contacts the threaded portion of the upper receiver.
Thread the barrel nut onto/into the threads of the upper receiver. Be careful not to cross-thread.
Hand tighten.
Step U4.5: Cycle the Barrel Nut
Attach the appropriate barrel nut wrench to a breaker bar. Tighten the nut lightly (about 25-30 ft. lbs.), and then loosen it. Repeat this 3-5 times. The cycling helps to ensure the barrel receiver extension is fully seated into the upper receiver before you torque it down.
Step U4.6: Torque the Barrel Nut
Aero Precision Enhanced Upper:
Set the torque wrench to 55 ft. lbs. (Aero Precision M4E1 Enhanced) or 65 ft. lbs. (Aero Precision M5 Enhanced) and attach the provided barrel nut wrench onto the square drive. Torque the barrel nut until the torque limit is reached. There is no need to worry about alignment of the barrel nut to allow the gas tube to pass through, as the gas tube passes through the handguard mounting lug, not the barrel nut.
Standard Upper:
Set the torque wrench to 30 ft. lbs. and attach an appropriate barrel nut wrench onto the square drive. If you are using an AR armorer’s tool, be sure to adjust the torque setting appropriately. Torque the barrel nut until the torque limit is reached.
You must now index the barrel nut appropriately. You can check alignment of the barrel nut using a barrel nut alignment tool, loose gas tube, or a #15 drill bit. Feed the gas tube surrogate from inside of the upper receiver. This must pass cleanly through the upper receiver and barrel nut.
Set your torque wrench to 80 ft. lbs. (YOU MUST NOT EXCEED THIS TORQUE). Begin to tighten the barrel nut a little at a time until the barrel nut indexes perfectly, allowing the gas tube to pass cleanly through.