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How to Build an AR (Part 4)

how to build an AR

Completing Your Custom AR Build: Fire Control Group and Butt Stock Assembly

Welcome back to the final installment of our custom AR build series! Today, we’re going to complete our lower receiver assembly by installing the fire control group and attaching the butt stock. So let’s dive right in!

Step 1: Assembling the Fire Control Group

The fire control group is a critical component of your AR, and it consists of the trigger, disconnect, and hammer. It’s essential to handle the springs carefully to avoid any issues with your rifle’s functionality.

First, let’s start with the hammer spring. Place the spring over the hammer, ensuring that it’s positioned behind the hammer, not in front. Next, attach the disconnect spring, making sure it fits securely into the trigger’s pocket. Afterward, install the trigger spring, again ensuring proper positioning.

Once all the springs are in place, align the trigger and hammer and carefully position them in the lower receiver. This step may require a bit of patience and adjustment to get everything lined up correctly.

Step 2: Installing the Safety Selector

With the fire control group in place, it’s time to install the safety selector. Insert the safety selector through the lower receiver. Place the safety detent, which looks like a tiny bullet case, into its designated hole. Then, insert the spring for the safety selector into the same hole. Align the pistol grip with the lower receiver, making sure the detent and spring fit correctly. Secure the pistol grip with the provided screw and star washer.

Function Test for the Trigger

Before moving on, perform a function test on your trigger. Make sure it works correctly in both the safe and fire positions. Additionally, check that the trigger resets as expected and that you cannot engage the safety when the hammer is in the forward position.

Step 3: Attaching the Butt Stock

Now that the lower receiver’s fire control group is complete, it’s time to attach the butt stock. Start by unscrewing the cap of the buffer tube, being careful with the spring inside. Next, take out the end plate and castle nut. Install the rear takedown pin, detent, and spring, ensuring they fit snugly into their designated holes.

Now, screw the buffer tube on, making sure it’s flush with the back of the receiver. Push down on the buffer detent and continue to tighten the buffer tube until you hear it snap into place. Check that the square nub aligns with the centerline of the gun. Tighten the castle nut over the end plate ensuring you don’t damage the spring for the rear pin detent with an armorer’s wrench and stake it in place using a small punch.

With the buffer tube and castle nut secure, it’s time to slide the mil-spec butt stock over the tube. Ensure it fits well, with minimal rattle. Perform a final check on the entire assembly to ensure everything is in place and tight.

Final Steps

Before heading to the range, perform a function check one last time to ensure the rifle operates smoothly. It’s also crucial to check headspace before firing the rifle.

Congratulations! You’ve successfully completed your custom AR build. Now, it’s time to take your new rifle to the range and enjoy the fruits of your labor.

Thank you for joining us on this custom AR build journey. We hope you’ve found our guidance helpful, and we wish you many enjoyable hours with your personalized firearm. Happy shooting!


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