Building Your AR Lower Receiver

So, you finally bought a stripped lower receiver and all the goodies that go along with it.

You excitedly tore open the box and checked to make sure we shipped you all the parts you needed to put together your first AR lower. You glare at the pile of parts and think to yourself, “Now what?”

Last year, we produced a series on how to put together the complete AR-15 lower receiver. As most of you know, the lower receiver houses the magazine catch, bolt catch, pivot pin, fire control group, trigger guard, selector, grips, pins and buffer tube.

We still field a ton of questions about how to put these parts together, so we thought a rehash was in order.

Installing these parts is fairly simple, and most people can do it without too many issues. However—when working on any firearm—if at anytime you feel you aren’t sure about what you are doing, take it to a qualified gunsmith.

Step 1: Installing the Magazine Catch

Step 2: Installing the Bolt Catch

Step 3: Installing the Pivot Pin

Step 4: Installing the Fire Control Group

Step 5: Installing the Trigger Guard

Step 6: Installing the Selector and Pistol Grip

Step 7: Installing the Takedown Pin and Buffer Tube

Stay Tuned!

Hopefully, this clears up some of the confusion. Once you do this a few times, most of the steps will become second nature. Stay tuned for more posts on AR builds. We’re going to pull some parts from the warehouse so we can throw together some uppers and barrels to see what we can come up with!

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 decisions. The information provided here does not represent the views of Cheaper Than Dirt!

Comments (47)

  1. When are you going to follow up with the barrel, gas tube, and hard sights installation videos to complete the build?

  2. Great videos. I noticed there was no mention of lubrication of the pins as I have seen other places. Necessary?

    1. Yes a drop of lube is appropriate. During the build its the best time to get protection into and on the small springs and detents. I can’t say your AR will get wet. I known mine get soaked, in the process of doing my work.

  3. Step 5, NEEDS to be changed.

    Never, NEVER, hit or try and drive in the trigger guard roll pin into a tab WITHOUT having something [such as the trigger guard itself] or a fitted block BETWEEN both tabs!!! They WILL BREAK OFF!!! If you can’t put the roll pin in place and drive it in by holding EVERYTHING IN PLACE, then place the lower receiver on a hard flat surface, such as a work bench, and put a small hard piece of wood UNDER the lower tab and the adjacent part of the rear lower receiver. NOTE – the lower tab, as the receiver sits on the work bench, should be flat on the piece of wood. If there is space on one side, find a different piece of wood or cut a piece to match the height of space between he work bench and the tab. DO NOT put the wood just under the tab itself. With the lower receiver sitting on the bench with the small block of HARDWOOD in place, AND the trigger guard in place, then, and only then, drive in the trigger guard roll pin.

    Again, NEVER, NEVER, drive in the roll pin without supporting the lower receiver [such as shown in the this video] AND having the trigger guard itself in place. You WILL break off a tab. I’ve seen it done!!!

    1. Excellent advice! That tiny discrepancy aside, this is an outstanding tutorial. After having been trained on the M-14, the first time I was issued an M-16 (AR-15) it seemed very complicated and I was a little intimidated. Wish I had this tutorial back in the day. Very well done.

    2. Very true Marine Gunner, these videos are SUPERB!! I shot an AR15 about 25 yrs ago and then never had the money to go out and just buy one till they came out with receivers and kits. Bought a receiver and a full kit a few years ago [upper was already complete and assembled] and then carefully laid everything else out on the work bench. WHERE to start, I thought!!! LOL!! With no instructions what-so-ever, just started visualizing where everything should go and how it should go together, then dove in!! Rather than driving in the roll pin for the trigger guard, I used a set of channel locks, and with the trigger guard in place, I squeezed the pin in place, AFTER oiling the heck out of it. It went in slicker than sh*t, or maybe I should say “snot on glass”, either way, it was a snap. 🙂 If any of you can get to a gun show, lower receivers are down to about $60 now and full complete kits can be picked up for less than $600, so there isn’t any excuses in not having an AR!! Happy Building!!!

    3. I just bought a Bushmaster AR-15 at the local Dunhams Sporting Goods store for $499. So for the best price I have ever seen on them I am now a member of the club. I put a 3×9 scope on it and laser bore sighted it. I love this gun.

    4. Doing my first AR lower build and finding the videos detailed and easy to follow. All the warnings about the trigger guard pins and broken tabs had me a little scared. As I intend to do several builds, I picked up a pin pusher for the trigger guard install. The pin pushing tool made the guard install fast and worry free.

  4. Really nice job on breaking down the assembly process into sections will have to check and make sure my MOE trigger guard came with that screw. Will be assembling my Lower tonight if my LPK arrives.

  5. these series of videos are excellentand cheaper than dirt has done an excellent job the technician who is working on the lower receiver did an excellent job its a gunsmith myself these videos are very handy and I’m glad that a wonderful company like cheaper than dirt have some available for beginners thank you cheaper than dirt for teaching other people this is there a little bit difficult but they can be accomplished by learning to your videos as a gunsmith for over 35 years I recommend cheaper than dirt with a big 10 and I am very glad they have these available for beginners novice and people who just want to learn how stoned rifles work you guys are wonderful and that’s why I like your company cheaper than dirt also carries for beginners novice advance and different rifles handguns also scope mounting so cheaper than dirt is a wonderful company or really Goes beyond the call of duty to help those for beginners those who have a little bit of experience and those who have a lot of experience so I’m very pleased with the videos as a professional gunsmith I recommend these videos for any person who wants to learn go to cheaper than dirt look at the catalog and you will find array of different items parts accessories and videos to help the new beginners and the old is a client from cheaper than dirt and a gunsmith recommend this company very highly also go to YouTube and you will find many more information on subjects as AR 15 ak-47s SKS is Mosin Nagants Mausers a lot of surplus rifles new your guns Glocks etcetera etcetera so enjoy yourself and remember 2 protects the Bill of Rights and the Constitution of the United States of America thank you very much to all of you out there who washes videos and learn about these wonderful things that we have in this country call the Bill of Rights and the constitution of this beautiful country of the United States of America cheaper than dirt has been around for a long time and is also highly recommended by the NRA there are a great company and I’m proud to have bought many parts from themI take this time to thank all of you and cheaper than dirt may God bless you all may God bless United States of America Sincerely Yours Jose angel Velez

  6. is the Takedown pin’s Detent pin and spring needed for proper operation? I have a Colt AR15 A2 Sport Comp. H Bar. And cant get it to cycle right on .223 ammo, I’m gonna try true 5.56 ammo to see if the higher powder load will allow it to cycle. I know My rifle was made in the 1980’s, so I’m thinking it was made for the higher powder loads of the 5.56 only. I can fire .223 but i have to re-cock it every time and clear the spent shell,(usually it jams the spent casing).

  7. Dennis, you need to have the stripped lower shipped to an FFL, the rest can just show up in your mailbox. That little chunk of metal (or plastic) is the “gun”, the rest are just “stuff”. With the chaos calming down (politics being political, something hotter always turns up) stripped lowers are again available for reasonable prices. CTD always seems to have a few choices on hand.

    And I do want a set on building an upper, please.

  8. Thanks for the video, it really helps out a lot. Now I feel I can do it one step at a time if I watch the video.

  9. HI, I am new at this, so I ask a Question. I know that to order a complete firearm, one must have it shipped to a FFL holder. Would it be possible for me to order all the parts so that I can build a completed unit without having a FFL. I would like to do this, but Have never done it , is there a site or page that shows everything necessary to do a complete build ?

    1. Also new to this, however it appears that the lower receiver, whether stripped or not, is what qualifies this as a firearm and thus must be registered (processed through FFL) The only way around (illegaly) would be to acquire the ‘lower’ personally through someone you know. Again, ILLEGAL!

  10. Videos were much clearer than what I’ve been able to get off of YouTube. Well done!

    I appreciate the efforts of people who post to YouTube, but sometimes, like trigger group installation, their hands actually cover up what they’re doing so you can’t, for example, see how the springs are oriented.

  11. Beautiful video, clear, concise, well filmed. I wouldn’t hesitste to tear open a box with a lower kit in it and start right on it. Thanx, great job.

  12. Thanks CTD more Info to help counts never ever stop learning or think we know it all! what we do not know we don’t we all have to start some where we need each other if Oboyo is re elected and becomes King of oboyo land forward the Omerica Flag of change we will !

  13. Excellent video. I would have included staking the castle nut as many people are unsure how to properly perform that operation or they use loctite that may be difficult to remove later on.

  14. Very good video. I agree with bill on the hex wrench. Being inside a cardboard box when you do it the first time, is not a bad idea. That little detent can make you sweat when you are looking for it on carpet. Voice of experience. And yes, I did find it after about 30 seconds of ‘very’ intense looking with a flashlight.

  15. Better, straight forward, and more clear than the out-of-date AGI video (I have it and too much BS in the video).

    Nice trick with the hex wrench for the pivot pin.

  16. Exactly what I’m looking for being this close to election time. Get that lower built so it can be grandfathered into a possible weapons ban

  17. Great basic information! Very helpful and appreciated. Many that own ARs are honestly too scared to do anything past a cleaning breakdown – this gives a chance to become much more comfortable with your firearm. Thanks!

  18. Castle nuts vary from manufacturer to manufacturer. I’ve read the reviews on all of the different wrenches that CTD sells, and all seem to fit different nuts on different brands. Are the teeth too thick or tall? Some other customers filed the teeth to fit their gun.

    It’s very common for this to happen. I use something very similar to this wrench on many builds, using the single ‘tooth’ part:

  19. Appropriate wrench for castle nut? I bought a Tapco wrench for my S&W AR15 Sport (mil-spec) and the wrench does not seem to fit castle nut. It seems that I will damage the nut and possibly the threads if I attempt to engage the wrench. What is wrong?

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