Installing a receiver extension (buffer tube) on your AR-15 can be quick and easy if you have the right tools. This guide will walk you through the steps and show the best practices.
Step 1: Prepare Your Lower Receiver
● Start by ensuring the firearm is unloaded and that there’s no magazine or ammunition nearby. Verify again that the lower receiver is clear and safe to work on.
● Remove any existing components if you’re replacing an old buffer tube. This includes removing the old buffer and buffer spring.
Step 2: Install the End Plate and Castle Nut
● Begin by threading the castle nut onto the receiver extension. Make sure it is oriented in the correct direction with the notches for the wrench facing to the rear.
● Then, place the endplate onto the receiver extension lining up the protrusion on the endplate with the groove on the receiver extension. Make sure the tab on the endplate is facing towards the lower receiver.
Step 3: Apply Aeroshell
● Apply Aeroshell grease to the threads on the receiver extension making sure to apply enough near the castle nut.
Step 4: Install the Buffer Retainer and Spring
● Thread the receiver extension onto the lower receiver until it starts to cover the hole for the buffer retainer pin.
● With a punch or similar tool, install the buffer retaining pin and spring in the hole and continue threading the buffer tube until the lip on the buffer tube captures the buffer retaining pin.
Step 5: Install the Takedown Pin
● Next, install the take down pin (rear pin) into the lower receiver making sure the groove for the detent is oriented towards the rear of the receiver.
● Install the detent and spring into the channel. Begin sliding the endplate towards the lower receiver and capture the takedown spring behind it. You may need to slightly rotate the receiver extension to make room for the spring and then rotate it back.
Step 6: Secure the End Plate and Castle Nut
Hand tighten the castle nut to hold the endplate in place. Set the torque wrench between 38 and 42 ft/lbs and torque the castle nut within that range. We recommend the Forward Controls Design Joint Castle Nut Wrench for best results.
Step 7: Staking the Castle Nut
● Using an appropriate punch, stake the endplate into the notches on the castle nut. We recommend the CNF from Forward Controls. Make sure to displace enough material into the notch to prevent the nut from rotating.
● After staking, apply a drop of Aluminum Black and wipe it off after 30 seconds. This will oxidize the endplate and gives it a black finish.
Step 8: Insert the Buffer Spring and Buffer
● Insert the buffer spring into the receiver extension, followed by the buffer. Ensure the buffer is secured by the buffer retainer and that it moves freely without obstruction.
Step 9: Test for Proper Function
● Always handle your firearm with care being sure the muzzle is pointing in a safe direction and wear approved shooting glasses and hearing protection when using your firearm.
● With everything in place, perform a quick function test. Pull back on the buffer and buffer spring to ensure they move smoothly. Check the fit and make sure there’s no wobble in the buffer tube.
● If possible, dry-fire your rifle to test the full cycling of the buffer system. Ensure the buffer spring compresses and returns to position smoothly.
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