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How to Build an AR-10: Tools, Parts, and Steps

How-To Guide for Building an AR-10

So, after learning about the differences between AR-10, DPMS Gen 1, and DPMS Gen 2 in our previous article, you’ve got your .308 AR 80% lower on the way to your front door, or you’ve already machined it. Congratulations!

Now that you’ve committed to an AR-10 build and you’re ready to machine that hunk of aluminum into a firearm, it’s time to actually put the weapon together. In this article, we will give you an idea of how to go about building an AR-10 with the right parts and tools.

AR-10 Build Tools List

.308 Easy Jig (80% Lower Jig) with Tooling

Besides the obvious (an 80% lower jig with tooling, like the .308 Easy Jig above) we built a list of some of the tools that you’ll need to complete your .308 AR.

AR-10 Build Parts List

Similarly, these are all of the parts that you’ll need to assemble your AR-10.

  • Lower receiver
  • Buffer, buffer spring, and stock
  • Lower parts kit to include trigger and pistol grip
  • Upper receiver
  • Barrel and barrel nut
  • Handguard
  • Bolt carrier group and charging handle
  • Gas block

Assembling the AR-10 Lower Receiver

Lower Parts Kit | AR-10 | CMMG

We recommend ordering a lower parts kit that includes everything you need in one package like the AR-10 CMMG Parts Kit above, but it is also possible to piece your own together. This one from CMMG is great because it is guaranteed to work with our DPMS Gen 1 80% lower.

Once you’ve got the parts, here’s what you’ll need to do:

  • Install your magazine catch on the left of the receiver. To do this, put the flat part in on the left side and install the spring on the threads from the right side. Tighten the button a few turns. Push the magazine catch further into the receiver with a pin or punch to be able to tighten it more. The bottom of the button should be flush with the receiver.
  • Install the bolt catch. Put the bolt catch spring and then the buffer into the recess on the left side of the receiver. Make sure the buffer is facing the correct way. Once it’s in place, put the bolt catch screw in place and tighten it.
  • Install the front pivot pin. Insert the spring first, and then the detent. Compress the spring, and insert your pivot pin with the help of your installation tool.
  • Install the trigger. Put the disconnector spring into the trigger, put the trigger spring in place, and put the disconnector in place. Drop the trigger into the receiver and put the trigger pin in place. Put the hammer spring on the hammer, put the hammer in place, and then install the hammer pin.
  • Install the safety selector, rear takedown pin, and pistol grip. Put the selector and takedown pin in place, and rotate the receiver over to put the detents and then the springs in place, and use the pistol grip to hold the springs in place. Install the screw to keep the pistol grip in place. Test the selector and takedown
  • Install the buffer tube. Thread the castle nut onto the buffer tube and put the end plate on. Start threading the buffer tube onto the receiver, and then put the buffer retainer spring and retainer into the hole at the rear of the receiver. Compress the spring and tighten the buffer tube until it holds the retainer in place, without pushing the nipple into the hole. Once the buffer tube holds the retainer down, tighten the castle nut the rest of the way. After it’s hand tight, tighten it using your armorer’s tool or castle wrench. Install the buffer spring and buffer.

Assemble the Upper Receiver

If you don’t order a complete upper, you’ll have to build your upper receiver. Buying a completed one may be slightly easier, but here’s a general guide for building an upper.

  • Install the ejection port cover. Get the pin started, line up the door, and push the pin through. At the halfway point, put your spring in the door, and then fully push the pin through.
  • Install the forward assist. Put the pin in place, put the forward assist in, and hold tension on the spring. Use the hammer to get the pin seated properly.
  • Install the barrel. With the upper in the vise, put the barrel in place and start tightening the barrel nut. Torque down as necessary.
  • Install gas tube and gas block.
  • Install the handguard.


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