What Your AR-15 Lower Build Needs

AR Lower Parts Diagram

You get a special connection with something you make yourself. This statement holds especially true with firearms. I’ve owned several AR-15s, but the one I pieced together is the one I keep at my side. I suppose the feeling of accomplishment has something to do with it. However, to be honest I just like telling people that I know how to put together a selective fire carbine. I have little or no mechanical talent, but this does not matter because piecing together an AR-15 is fairly easy—just don’t tell anyone how simple it is! All parts of an AR-15 are important, but the components that make up the lower receiver are especially crucial. The lower receiver attaches to every other major component of the gun, and a stripped lower receiver is the only portion that BATFE considers an actual firearm. You don’t need much to complete your lower receiver. Most parts are inexpensive and easy to come by in today’s market.

The Building Blocks

Stripped lowers vary in price greatly. However, as long as your receiver is in specifications and properly machined, you won’t have any issues. I own both aluminum and polymer lowers, and both perform very well. With few exceptions, even the low-cost bargain basement lowers to just fine. When you find a deal on a stack of lowers, move on it. I don’t really care what rollmark is on the side. As long as the gun cycles, I’m happy.

Lower Parts Kit

There is really no need to buy each pin and catch individually. Extremely high quality parts kits are easy to come by and rarely have issues. Inspect the packing list on the kit you are buying to make sure it has the following: AR Lower Parts Diagram

  1. Bolt Catch
  2. Bolt Catch Plunger
  3. Bolt Catch Roll Pin
  4. Bolt Catch Spring
  5. Buffer Retainer
  6. Buffer Retainer Spring
  7. Disconnector
  8. Disconnector Spring
  9. Hammer
  10. Hammer Pin
  11. Hammer Spring
  12. Magazine Catch
  13. Magazine Catch Button
  14. Magazine Catch Spring
  15. Pistol Grip
  16. Pistol Grip Lock Washer
  17. Pistol Grip Screw
  18. Pivot Pin
  19. Pivot Pin Detent
  20. Pivot Pin Detent Spring
  21. Selector
  22. Selector Detent
  23. Selector Detent Spring
  24. Takedown Pin
  25. Takedown Pin Detent
  26. Takedown Pin Detent Spring
  27. Trigger
  28. Trigger Guard
  29. Trigger Guard Roll Pin
  30. Trigger Pin
  31. Trigger Spring

Stock Kit

To complete your lower receiver build, you will need a stock assembly. This should house your buffer tube, stock, buffer spring, castle nut and receiver extension. Stocks come in all shapes and sizes, but few complain about a basic collapsible model. Even the entry-level versions hold up well. Some choose the A2 style, which do not adjust to size, but give a solid shooting platform in return. I should note that an AR-15 multi-tool helps immensely with that castle nut, as well as several other common AR adjustment jobs.

The parts listed above are mostly for a basic AR build. There are different trigger groups, fancier stocks, buffers and widgets you can get as upgrades to just about everything here. That is part of what makes an AR so much fun. The modular design makes it the most customizable firearm on the market, which you can spend countless hours improving.

The Mission of Cheaper Than Dirt!'s blog. "The Shooter's Log", is to provide information - not opinions - to our customers and the shooting community. We want you, our readers, to be able to make informed decicions. The information provided here does not represent the views of Cheaper Than Dirt!

Comments (18)

  1. I am wanting to buy a parts layout print. Do you have them for sale and if not could you tell me where I could get one. The one shown in this article is exactly what I need.

  2. I’m really suprised by some of these comments.Some of you people need to do a little research and understand the basic functions of an AR15 before you make such stupid remarks.

  3. I would love to build one and hope to be able to do so when parts are available again. I enjoyed the read and will put it to use if I can get the parts. Thank you!!!

  4. I wish I had this list when I began my lower build project last year. I had to compile mine myself from the internet (including youtube) and several online sources. The only suggestion I would make is that kits are available that do not include the pistol grip or trigger assemblies, which are parts that many will want to buy separately. Similarly, buffer assemblies can be purchased that do not include the stock, but be sure you order either a mil spec or commercial buffer tube and stock (although some stocks will adapt to either standard). You will also need a few tools. I found these to be essential (or at least, useful): AR15 Roll Pin Starter Punch Kit, Pivot Pin Dent Installation Tool, Roll Pin Punch Set, Lower Receiver Vise Block, and – as mentioned – an AR15 Combo Wrench.

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