Final Assembly (AR-9, AR-15, and AR-10/LR108)
If you’ve come this far, you are only moments away from your fully-assembled AR. In this section, we will cover the final assembly and function check of an AR.
Step F1: Move Pivot and Takedown Pins to Open Position
Push the pivot and takedown pins from the left side of the lower receiver until they click out of the closed position. Extend the pivot and takedown pins to the full-open position.
If you have trouble opening the pivot and takedown pins, the detents may be having a hard time moving out of the recess in the detent channel. Tap the left side of the offending pin with a non-marring (i.e. nylon or rubber) gunsmithing hammer$ head. Once you are able to open the pins, add a drop of wet lube$ into the detent channel using a needle dropper$ and cycle the pin open and closed a few times.
Step F2: Place Upper Receiver Onto Lower Receiver
Insert the pivot and takedown lugs on the upper receiver into the lower receiver.
Step F3: Close Pivot and Takedown Pins
Press the pivot and takedown pins to close them fully.
If you have trouble closing the pivot and takedown pins, try adding a drop of wet lube$ into the detent channel using a needle dropper$ and cycling them open and closed a few times.
If you are unable to close the pivot and takedown pins with the receivers mated, verify that the holes in the upper receiver lugs are properly aligned with the holes and pins in the lower receiver. You can view the path of the pins from the left side of the receiver. If you don’t see a clean path (i.e. the holes don’t line up), there may be a problem with your upper and/or lower receiver. Hopefully, you heeded our advice on inspecting for this defect BEFORE you assembled your receivers.
Step F4: Function Check
Now that everything is where it should be, its time to make sure everything moves like it should. We have a specific regimen to ensure everything functions, dry.
Step F5: Give Yourself a Pat on the Back!
If you’ve made it this far, you’ve completed the final assembly of an AR and you’ve built a firearm. Congrats!
Now head to the range and start shooting!