AR-15 Assembly

The entire assembly process, presuming you have ordered the pre-assembled barrel parts, will take you no longer than an afternoon--2 hours if you are good with mechanical parts and at following schematic diagrams. Again, here the USMC Technical Manual is essential, providing invaluable diagrams and schematics.

Read the USMC Technical Manual through once, then twice. After which, you will understand and have an overview of the entire project. Really, it comes down to fitting some parts together and using roll pins to put the rifle together.

If you have ordered the parts as described above, then your Upper Receiver and Barrel Assembly comes pre-assembled, and has generally been test-fired at the factory. It is a good idea to confirm this when you order from your parts supplier that, in fact, your Upper Receiver and Barrel Assembly has been tested for headspacing and test-fired. This dispenses with your need to test the headspacing of the chamber—though it is a good idea to have and occasionally use a "FIELD HEADSPACE GAUGE" (available at Brownells and other parts supplies for about $15.00). It will come with instructions on how to periodically test your headspace to assure the safety of firing your AR-15 rifle.

I read a suggestion somewhere that you should put down and spread out a few large, spare white sheets in your living room or garage to keep from losing parts upon assembly. I have personally used this method, and have found it to be a great idea. Also, have a few paper plates ready to put all your little springs and detent pins into until they are ready to be used. Clean all your parts first with Breakfree CLP or like product—and if you have time let the parts soak overnight.

Also, please remember to wear safety glasses when you are assembling your rifle. All the little pins and springs become mini-projectiles that are a ballistic liability to your eyes! Trust me, I’ve had one or two close calls, being too cool to wear safety glasses in the presence of no one in my own garage. I now wear them whenever I work with the pins and springs!

There is one tricky part in the assembly process. This is the front takedown pin’s detent spring and detent pin installation. This requires some patience and a few attempts. Brownells sells a special tool for this project. It is worth it the $7.95 if you are intending ever to construct 2 or more rifles. Otherwise, use a blade of some type, and be extremely careful of losing the spring and detent pin when installing them!

(Note: One major discrepancy in the USMC Technical Manual’s instructions with regard to your semi-automatic version is the section on installing the firing control group and safety selector assembly. Simply forget about the USMC Technical Manual’s instructions regarding "automatic sear parts" installation, and the rifle will still come together fine. You may notice that your "safety selector switch" remains loose and free-moving after installation of the firing control group and safety selector assembly. Don’t worry, upon installation of your pistol grip, the safety selector switch will tighten up and function reliably.)

After assembly, you are ready to shoot your new rifle. Remember to properly break-in your rifle’s new barrel.