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One of the reasons the AR-15 platform is its modular design which allows for a tremendous amount of flexibility in what the owner can do to make it their own. As much as the minutemen of yore customized their muskets to suit their personality, so too can the shooter of an AR-15 rifle. Many people will buy an off the shelf AR-15 and add sights, lights and other accoutrements, but many will go the extra mile and build theirs from the ground up. This page is for those hobby gunsmiths who want to build their own AR-15. While some folks like to build both their upper and lower receivers, its more common to build your lower and just snap what ever upper receiver you choose onto the new lower.

Things you will need:

1. A stripped lower receiver: Traditionally these are aluminum but I have chosen to build this one from a GWACS Armory Cav-15 polymer receiver.

2. A Lower Parts Kit. Most of them come with everything you need except the stock. In this case because the Cav-15 receiver already comes with a pistol grip, stock and pins, I will have some parts left over.

3. Tools: Ball peen or plastic hammer, a set of punches, small flat head screw driver, c-clamp or other device to press pins and a lower action block.

1. Get your favorite lower receiver. Whether its aluminum or polymer like this GWACS Armory CAV-15 MKII makes little difference. We carry both types or you can order one from your preferred vendor and we can do the FFL transfer for you.

2. Lower Parts Kit: There are many lower parts kits out there. This one is from DPMS. GWACS Armory has ones that do not have the parts that are not needed on their receivers.

3. Magazine Catch Assembly: Insert the Magazine Catch into the left side of the receiver. Hold it in place with your finger and flip the receiver over. Place the Magazine Catch Spring over the threaded pin. Compress the spring with the Magazine Catch button.  As you press the button and spring, allow the Magazine Release Catch to slowly lift away from the receiver. This will allow you to turn it clockwise, threading it through the button. Thread it until the top of the catch is flush with the top of the button. Function check the assembly. Make sure that the magazine catch clears the interior of the magazine well.

4. Bolt Release Assembly:  This one is a little tricky due to the small spring involved and the location of the pin. Insert the small end of the Bolt Catch Buffer into the Bolt Catch Spring (make sure you do not confuse this spring with the Disconnector Spring which is tapered). Insert the assembly into the left side of the receiver. Align the hole of the Bolt Catch with the holes at the top of the receiver and press or drive the Bolt Catch Roll Pin into the receiver. Using a plastic hammer or a wrapped hammer or clamp will prevent you from marring the finish of the receiver.

5. Trigger Group Assembly:  Hook the two hoops of the Trigger Spring over the pin holes of the trigger. Insert the Disconnector Spring into the top of the trigger housing and place the Disconnector over the top of that. This part of the assembly is a little tricky because the hole in the disconnector must align with the holes of the trigger housing and the holes in the receiver. Some jiggling will be required… It helps to start the Trigger Pin before inserting the assembly. Once the holes are lined up press or drive the pin into place until it is flush on both sides.

Hammer: Hook the two hoops of Hammer Spring over the pin holes of the Hammer. Make sure the long legs stick out from the bottom and the closed end is on the back.  Insert the assembly into the top of the receiver.  The long legs of the spring will set into the rear of the receiver housing, behind the ears of the trigger assembly. This will provide the tension the hammer needs to operate. Press the hammer down and in until the pin holes align with the holes in the receiver and press the hammer pin in. Armorer’s note from GWACS Armory:  “Hammer Pin will be recessed on both sides. Insert until “J-pin” engages center notch. Function check the assembly. Cock the hammer back. The sear on the disconnector should grab the hammer. Hold the hammer and pull the trigger. The sear should release the hammer and allow it to snap forward. DO NOT allow the hammer to drop freely. The force may break the bolt release.

6. Safety Assembly: Unlike traditional aluminum receivers (the safety detent and spring load from the bottom and held into place when the pistol grip is installed), the Safety Detent Spring the Safety Detent load from the top of the receiver. A number 27 drill bit may be required to open the hole large enough to allow the detent to drop in. It may also be necessary to trim the spring to allow the Safety Selector to insert. Trim only small amounts and test to avoid removing too much spring which will affect the tension on the Selector. Use the small flat head screw driver to compress the spring enough for the selector to clear the detent and snap into place.

7. Buffer Assembly: The CAV-15 MKII uses a carbine buffer and spring.  GWACS Armory sells a buffer and spring set that looks so nice, its actually a shame you only see it when the upper receiver is removed. GWACS Armory provides a roll pin to hold the Buffer Retainer Pin and Spring in place.

Insert the buffer spring into the stock. Press the buffer and spring into the stock. Use your thumb to press the assembly just past the hole where the retainer and spring will go.. Insert the buffer retainer spring and buffer retainer into the top of the stock until just the tip is exposed. Gently release the buffer until it contacts the top of the retainer. The retainer will prevent the buffer from shooting out and the buffer will prevent the retainer from shooting out.

Use the hammer and pin punch to drive the provided roll pin into the stock until it contacts the retainer. Use the small flat head to slightly depress the retainer and hammer the pin the rest of the way in. The pin will prevent the retainer from getting lost when the buffer is moving or removed.

Parts Not Used: Front and Rear Takedown Pin Assemblies, Trigger Guard and Pin, Pistol Grip and Bolt.

Disclaimer:

Possession and/or ownership of firearms is subject to various federal, state, and local restrictions, laws and regulations. Buying, carrying, or using a firearm without compliance with local, state, and federal law is a crime. It is your legal responsibility to learn and obey the laws that apply in your area. The assembler has complete responsibility to ensure he/she is in full compliance with all applicable local, state and federal law regarding possession of firearms. Gresham Armory LLC . Further, the assembler assumes any and all responsibility to insure any firearm purchased is handled safely. GRESHAM ARMORY LLC SHALL IN NO WAY BE LIABLE FOR ANY SPECIAL, INDIRECT, PUNITIVE OR CONSEQUENTIAL DAMAGES RESULTING FROM ANY USE OR MISUSE OF ANY INSTRUCTIONS FOUND HERE. THE BUILDER IS RESPONSIBLE FOR ANY INJURY OR DEATH RESULTING FROM IMPROPER ASSEMBLY OR USE OF ANY FIREARM BUILT USING THESE INSTRUCTIONS.