How to Assemble an AR-15 Lower

Lay out all your parts on a table with a white surface. Wipe off any excess oil from the parts, and check against the manifest that came with the AR-15 that all parts are present. Check your receiver to make sure it has no damage or grime; clean the receiver if necessary. Place each part, by type, into a plastic container to prevent it from rolling away or being brushed off the table while you work.

Locate the magazine catch screw and put it into place on the receiver, on the left. Thread the magazine catch spring onto the magazine catch screw, from the right side of the receiver. Screw the magazine catch button onto the screw for three or four turns. Use your drive pin punch to screw the button into the side of the receiver, stopping when the button is tight. Press the button to check that it pushes away the magazine catch screw and that the spring returns it.

Attach the trigger guard to the receiver. Place the trigger guard into the fork beneath the trigger, and align the holes. Place a roll pin into the top of the fork and, using the drive pin punch and a hammer, slowly push the roll pin through the trigger guard&'s hole. Tap lightly with the hammer and avoid forcing the roll pin. Repeat on the other side of the receiver.

Install the bolt catch. It will be just above the magazine catch. Place the spring in the hole on the left side of the receiver. Slide the bolt catch plunger into the spring, round end first. Place the bolt catch in the fork above the magazine catch and slowly place a roll pin into the hole to secure it, using a drive pin punch. Check the bolt catch to make sure the spring has strong tension.

Ease the trigger spring onto the trigger, with the ends of the spring under the trigger and facing forward. Place the disconnector spring into the fork on the back of the trigger. Place the hammer pin on top of the trigger assembly, and place the entire assembly inside the receiver. Slowly tap in the trigger retaining pin. Pull the trigger a few times to ensure it is operating smoothly.

Install the hammer spring on the hammer. One leg of the spring should point forward on the left side of the hammer, and one backwards on the right. Place the hammer in the receiver, and use the hammer retaining pin and the drive pin punch to secure the hammer in the receiver. Work the assembly to ensure the hammer is functioning properly. Then cock back the hammer and insert the selector on the left side of the receiver, pointing up in the "fire" position. Bolt on the grip and the stock, and your lower is complete.