Assembling an AR-15 Lower Receiver

This week we are assembling an Radical Firearms AR-15 Rifle. We started with an incomplete lower and, piece by piece, turned it into a fully functioning rifle. By ‘we’ I mean Kyle, because I had no idea where to start.

Parts List:

UTG PRO AR-15 Position Mil Spec Buffer Tube Hiperfire AR-15 Sharp Shooter Trigger Assembly Anderson Manufacturing Buffer Tube Assembly Kit with Stock Anderson Manufacturing Lower Parts Kit Radical Firearms 10.5” 5.56 Nato Upper with Bolt and Charge Handle Mission First Tactical 30-Round AR-15 Magazine (pinned to 5) Ergo AR-Wedge (Don't see the part you're looking for? Contact us and we can order it!) One of the first tips Kyle gave me for assembling any sort of firearm is to be very careful because once a spring or pin falls on the floor, it can be almost impossible to find. Even being cautious, we still dropped one piece. We did find it!

How to  assemble the safety and grip:

Small screw being held with Locktite applied.We started with the safety which was part of the Anderson Manufacturing Lower Parts Kit. Kyle used Locktite on all of the screws so that they won’t come loose through repeated firing. Our second step was to attach the Pistol Grip to the Lower Receiver. The Fire Control Selector Spring slides into the Pistol Grip at the top, and the Fire Control Selector Detent sits on top of it. These pieces are the final bits of the safety. Once the pin and spring are in place, you hold them down until the grip is held tight against the Lower Receiver. There’s a bigger screw and washer that goes up inside the grip to secure it into place.

Adding the pivot and takedown pins:

We moved on to the Pivot and Takedown Pins. There is a small Detent and Detent Spring which slide up into the Lower Receiver and need to be installed to ensure that your pins don’t pop loose when you disassemble your gun. Ar-15 stock Dentent Springs and Detent Pins are very tiny. We recommend working over a cloth to help catch any wayward parts. The Detent Springs and Pins can be tricky to wedge into place; after you slide them into the receiver, you must hold them in place while you insert the Pivot or Takedown Pin. You may find it useful to use a flat tool to keep them wedged in place while you do this. Detent pin, spring in receiver, Take down pin

How to assemble the magazine release:

The next piece we installed was the Magazine Release. It is comprised of three components: The Magazine Release, the Release Spring, and the Release Button. The spring sandwiches between the two parts inside the body of the Lower Receiver. The Release Button tightens down on the Magazine Release and holds everything in place.

Buttstock and Buffer Tube Assembly:

Lower receiver, castle nut, buttstock, receiving plate, buffer tube assembled.After that, we changed direction and assembled the Buttstock and Buffer Tube. The kit came with a grey Buffer Tube, but we swapped it out for a blue part from UTG. The Buffer and Action Spring are critical components for managing recoil and seamless firing. The Action Spring slides in first and the Buffer follows it. The non-threaded side of the Buffer Tube slides into the Buttstock and is held in place by the Lock Release Lever. To insert the Buffer Tube, you have to pull the pin down fully then slide the Buffer Tube into the Buttstock. The Castle Nut screws onto the Buffer Tube first, then the Receiver End Plate is sandwiched between it and the Lower Receiver. We dropped in our Buffer Retainer and Buffer Retaining Spring then held them down while we screwed in the Buffer Tube. After screwing the Buffer Tube into the Lower Receiver, we tightened down the Castle Nut.  

Bolt Catch

Bolt Catch being inserted into Lower ReceiverBack to the Lower Receiver -- we attached the Bolt Catch next.  The Bolt Catch Pin and Bolt Catch Spring fit inside the receiver and the Bolt Catch fits on top of them. There is a small pin that must be hammered into place. This Bolt Catch Pin holds the Bolt Catch to the Lower Receiver. To protect the Lower Receiver from unintended dings or scrapes, we covered it in tape during this step and used a very small mallet.   After that we installed the Trigger Guard Assembly. The Trigger Guard Plunger and Spring are wedged into the Trigger Guard Assembly, then the guard slides into the Lower Receiver. A pin is fitted to hold the guard in place.

Trigger Assembly

We chose to use a Hiperfire AR-15 Sharpshooter Trigger Assembly. This part was incredibly easy to install and had two pull weights from which to choose. The trigger came pre-assembled with this kit. We simply dropped it into place and used the drifting pin provided to swap out their place holder pins for the longer pins that hold the assembly in the firearm. This saved us from having to hold multiple parts in perfect alignment while we hammered the pins through the Lower Receiver and Trigger Assembly. Hiperfire Trigger Assembly Parts

Final Steps

Before attaching the Radical Firearms 10.5” 5.56 Nato Upper Receiver, we inserted the Ergo AR Wedge. This little piece ensures that the fit between the Upper Receiver and Lower Receiver is tight. Wedge inserted into receiver   With our installation complete, it was time to test fire the rifle! We didn’t bother attaching a sight for our test as we were more interested in making sure all our connections were tight and all the pieces were functioning as intended. Firing the AR-15 in our RangeKyle showing off the functional AR Rifle After building out your Lower Receiver into a fully functional firearm, don't forget to verify and confirm with the RCMP in Ottawa that it is approved.