This post includes the full video and links to all the tools, parts, and other goodies that YouTube doesn't allow.
The Tools I Use To Build AR-15 Lower Receivers
- Real Avid Master Armorer’s Kit
- Non-Marring Hammer (The Real Avid armor’s wrench is also the hammer.)
- AR-TT (AR Takedown Tool)
- Precision Screwdriver Set (For the trigger guard set screw and other small screws)
- Knipex 10″ Wrench Pliers (For the bolt catch and trigger guard roll pins)
- Gun Oil (Lube as you build, so you don’t have to do as much later.)
- Razor Blade (For the pivot pin spring and detent)
- AeroShell 33MS / 64 Gun Grease (For the castle nut and buffer tube; also for barrel nuts)
- Birchwood Casey Aluminum Black (For repairing scratches and blemishes)
- Needle Nose Pliers (For holding roll pins)
- Roll Pin Specific Punches (Makes driving roll pins suck less)
- Deck Of Playing Cards (To use as shims to support the receiver if you don’t have a dedicated bench block or vise)
- Inch Pound Torque Wrench (For the grip screw and trigger/hammer pin screws)
- Blue 242 Loctite (For the larger screws)
- Purple 222 Loctite (For the small screws)
Buying vs Building Your Own DIY AR15 Lower Receiver
The AR-15 is the most popular firearm in the United States. There are tons of companies that build complete rifles and offer all kinds of build-your-own kits. If you’ve never owned an AR-15 before, the idea of building one from scratch may seem a little overwhelming.
Buying a complete rifle is a great option, but building your own can be a lot of fun! It can also save you quite a bit of money. There is nothing quite like building your own gun, plus you have full control over the final design. You can assemble a stripped lower receiver and then buy a complete upper receiver for it. That way, the majority of accuracy and reliability-producing parts are professionally assembled.
Whether you’re a first-time AR-15 builder or a seasoned pro, this post is for you! This guide will help you through the process, including photos to reference.
The lower parts kit I used for this project was provided by Palmetto State Armory, and I am affiliated with PSA. All the links below are affiliated, which means I get a small commission if you order something. Don’t worry, there is no extra cost for you; it just helps keep the lights on around here.
The CMC Trigger Sets This Kit Apart
These steps are the same for other lower parts kits on the market, not just this PSA kit. The only major difference between this kit and other lower parts kits is the trigger. Most lower receiver build kits come with mil-spec fire control groups. That’s the fancy name for the trigger and all the springs and stuff that makes it work. There are eight individual parts in a standard mil-spec fire control group. The CMC trigger in this kit is self-contained and simply drops into your lower – no need to fuss around with weird springs, annoying pins, or tricky alignments.
The trigger is also one of the first parts that people tend to upgrade when they start tinkering on their builds. With this PSA kit, you can skip the mil-spec trigger and go straight to a wicked, smooth CMC trigger.
The kit comes with everything you see here except for the lower receiver. Since it doesn’t actually contain a firearm, it can be shipped directly to your house from PSA. No need for an FFL, since the “firearm” is a stripped lower receiver that you already have. This kit has all the springs, detents, and other parts needed to complete an AR-15 lower receiver. Tons of upper receivers are available from Palmetto State Armory too. They also have upper receiver build kits and lower parts kits, if you’d prefer to assemble your own.
Tools Needed To Build Your Own AR-15 Lower Receiver
You will need a few tools to get this done. As with most things in life, you tend to get what you pay for… When it comes to tools, they can vary widely in quality. They can also mean the difference between a fun build and a new hole in your wall…
I primarily used Real Avid products for this build, and I’ll continue to use them in future builds. I’m not sponsored or affiliated with Real Avid in any way. I just happen to like them a lot, and you can see why by watching the video. Recently, we’ve started stocking Real Avid products for our store, which you can find here.
All the Real Avid tools you’ll see, minus the Master Gun Vise, came in the Master Gunsmith kit. If you’re planning on building a lot of guns, or if you’re looking to upgrade some older tools, this kit is a great option. Brownell’s also offers an all-in-one type of armorer’s kit, although it is quite a bit more expensive.
Other brands known for gunsmithing tools include Brownell’s, Wheeler Tools, Fix-it-Sticks, and NcStar. It’s usually cheaper to go ahead and buy a gunsmithing kit, rather than trying to get individual tools, especially if you don’t currently have any gunsmithing tools at all.
One of the cool things about building your own lower receiver is that it saves you money. If you use some of those savings to buy tools, you now have a sweet DIY gun and tools you can use for all your future builds. Nice!
AR-15 Armorer's Wrench
If you decide to pass on picking up a complete gunsmithing kit, you can get away with most of the steps with tools you probably already have on hand. Really, in general, you can build an AR-15 lower receiver with basic hand tools.
The only real required tool is a castle nut wrench. If you don’t have a proper armorer’s wrench, properly tightening your castle nut on your lower receiver is going to be extremely difficult. You’ll also most likely end up damaging something or hurting yourself in the process. Here are some great options for armorer’s wrenches, if you don’t have one yet.
There are also cheaper options available (on Amazon, for example), but I personally would not recommend them because of the following reasons:
- Only one purpose (castle nut)
- No barrel nut wrench
- No place to attach a torque wrench
- Very thin profile, so it easily slips off the castle nut, causing damage
- No way to accurately tighten the nut to the required specs
- Made from cheap Chinese sheet metal
- No ability to use as a hammer
- No muzzle device wrench
Another tool that will come in very handy when building an AR-15 lower receiver is a bench vise. It doesn’t have to be a super fancy, multi-axis, master-level vise, but some kind of vise to hold the lower will be very helpful. Obviously, something like the Real Avid Master Gun Vise is awesome, but you can get away with a fairly basic vise, if money and/or available space is tight.
Here’s a “good, better, best” set of options, if you need to pick one up.
Lower Receiver Vise Block
Along with a bench vise, it’s best to use a lower receiver vise block with it. If you don’t use a vise block, you can seriously damage or even destroy your brand new lower. Vise blocks come in all kinds of shapes and sizes, as well as different price points. Most of them use the magazine well as the primary attachment point. You can honestly get away with almost a complete lower receiver build without a vise and vise block. The part that will be very hard to actually get right without a vise is the castle nut and receiver extension. If you don’t have a solid way to hold the lower in place while you apply torque, things can get squirrely.
For me and this guide, I prefer using the Real Avid Smart Vise Block. The reason I like this block is that it can be tightened down in the magazine well and hold a completely stripped lower receiver rock solid. It also comes in the Real Avid Armorer’s Master Kit. Most other vise blocks rely on the magazine catch to be installed and don’t actually hold the lower with anything other than friction and the magazine catch spring.
The only other lower receiver vise block I would bother taking a look at is from Midwest Industries. Their AR vise block holds the lower by the magazine well with friction. It can also be used to hold the lower for your fire control group, trigger guard, AND gas block installation. Very cool!
Step One: Install The Magazine Catch (AKA Magazine Release)
The first part we’re going to install is the magazine catch. This is also the magazine release, depending on how you want to look at it.
Insert the magazine catch in the left side of the receiver, through the hole in the middle.
Next, place the magazine catch spring over the shaft of the magazine catch from the other side of the receiver. The magazine release button is going to thread onto the magazine catch.
Make sure the textured side of the magazine release button is facing out. This step works best if you push in and hold the magazine release as if you were ejecting a magazine.
That allows the catch to spin freely on the other side of the receiver and not bind up on the spring. If you try to tighten the magazine release button at this point, it will bind up on the spring, which is annoying. Not to mention, you can damage the spring by doing it that way.
When you press the magazine release button, use either a punch or tweezers. Push the release button into the receiver and compress the spring. Then rotate the magazine catch clockwise to tighten it.
Test fit several different magazines to make sure they lock into the receiver, as well as drop easily.
By installing the magazine catch first, the lower receiver can be locked in a vise to stabilize it. This is one of the reasons I prefer Real Avid over other vise blocks on the market. The Real Avid Smart Vise Block can lock a completely stripped lower receiver down. The base of it interfaces with the jaws of the Real Avid Master Gun Vise perfectly too.
Step Two: Install The Pivot Pin
The next step is installing the pivot pin. This is one of the parts that can be a little tricky to get right on your first try. The difficulty comes from compressing the spring and detent without letting them fly across the room. PSA is kind enough to include an extra spring and detent, in case you launch a set into orbit.
Let me introduce you to the AR Takedown Tool. This is a brand new tool on the market, made in the USA. It’s a dual-sided, spring-loaded brass punch that includes a removable small pin. This tool was provided to me from AR-TT.
The AR Takedown Tool is super handy for installing the pivot pin because it allows you to capture the spring and detent. There are several other tools designed specifically for the pivot pin. Real Avid includes a pivot pin installation tool in the Master Armorer’s kit. There are also a few other tools on the market, designed to make installing the pivot pin easier.
I opted to try out the AR Takedown Tool for this build. You can also use a 1/4×2″ clevis pin that you can pick up for around $2 at your local hardware store. Here is a video I made a while back, going into more detail on the clevis pin hack.
What you’re trying to do is put your spring and detent into the front of the receiver without launching parts into space. With the AR Takedown Tool, you slide it in from the right side, so that hole in the AR-TT is directly over the hole in the receiver.
Next, take the pivot pin spring and insert it through the AR-TT into the lower receiver. Then, install your detent with the pointed side facing out.
Once you get the spring and detent in place, unscrew the front part of the AR-TT tool (the small part). Push the small pin through the AR-TT just far enough to push the spring and detent into the receiver. Next, rotate the AR-TT 90 degrees, so the hole is vertical. The spring and detent will be captured in the receiver by the AR Takedown Tool and won’t go flying across the room.
To install the pivot pin, orient it so that the cutout part is facing the back of the receiver. Hold pressure on both the pin and the AR Takedown Tool at the same time, while sliding the pin over. Keep pushing them together, until you hear the pin click into place. Now, the spring and detent are capturing the pivot pin.
Another option I’ve seen before is using something like a razor blade to depress the spring. If you use a thin enough blade, you can slide the pivot pin over it and then pull the blade out. I haven’t tried that method yet, but it seems to be a good option, if you don’t want to buy a new tool.
Leave a comment if you’ve ever embedded a detent in your ceiling!
Step Three: Install The Bolt Catch
There are a lot of different ways to install the bolt catch roll pin. The main idea is to try to do it in a way that doesn’t scratch the receiver.
Below is the Real Avid Master Bench Block. As you can see, there are a lot of cutouts and grooves to do all kinds of work on stripped uppers and lowers. It’s also designed to do work on bolts and the charging handle. This armor’s block has a slot for the pivot pin to lock into the block vertically, which is why we installed that pin before the bolt catch. This will keep the lower receiver from tipping one way or the other, when you’re installing the bolt catch roll pin.
Now, with the receiver locked to the block via the pivot pin, we’ll install the bolt catch. This is one of the more difficult steps, and the receiver can get damaged a little in the process. I recommend protecting the finish of the receiver with some masking tape.
The bolt catch is going to be installed on the left side of the receiver, just above the magazine catch we installed earlier.
The punches I’m using for this are the Real Avid bolt catch punch set. They’re actually milled off about halfway through on one side, so you can hammer them around the back of the receiver.
The bolt catch roll pin has to be installed from the back of the receiver. If you try to install it from the front, it’s going to start at a slight angle and do a lot more damage than if you go from the back. That can bend the pin, break the ears the pin is going into, and generally make a mess.
This roll pin punch starter is basically a hollow punch that holds the pin in place, so you can get it started. At a certain point, that particular punch will not drive it any further. Either switch to another punch, or another tool that I’ve found to be really effective, is actually using some pliers. Knipex wrench pliers do really well for this job because, as you squeeze the pliers, the jaws remain perfectly parallel. That allows you to squeeze the pin into place perfectly even.
If your receiver gets scratched up, you can use aluminum black to make it look new again. This stuff is super handy, if you’re not exactly accurate with your hammer work. On the other hand, if you don’t mind scratches, no worries.
Step Four: Install The Trigger Guard
The back of the trigger guard is the fatter part that goes towards the grip. The set screw comes preloaded with a thread locker from Magpul and just screws right into the receiver itself.
Now, the tricky part again is the roll pin. This is very similar to the bolt catch roll pin. I used the tweezers from the Real Avid Armorer’s Master Kit to hold it in place and then gave it a little tap to get it started.
You should support the ears of the lower receiver around the trigger guard while you do this. If you don’t, you can actually break them off and ruin your receiver. The Real Avid Master Bench Block has a cutout specifically for this. If you don’t have a bench block, you can also use a deck of cards to make layers and support the lower while you work on it.
Using the AR Takedown Tool (the wider end), it’s kind of self-centering, as you pull back the spring and let it go. It basically acts as a hammer and punch all in one, and it works really well.
Step Five: Install the Trigger
This PSA kit features a CMC 3.5lb flat face drop-in trigger, which makes it extremely easy to install. It also has a very clean break and is a lot of fun to shoot.
The trigger is where this particular kit from Palmetto State Armory really shines. Normally, installing the trigger is a difficult part of an AR15 lower receiver build.
In this case, you can see how the trigger is completely self-contained in its own little box. To install it, just cock it and slide it into place. Because all the springs and small parts are self-contained, the trigger is now the easiest part to install!
The trigger and hammer pins are smooth and identical, so it doesn’t matter which one goes where. They have set screws on both sides, so they slide right in and then are held in place by the set screws.
This is by far the easiest trigger that I have ever installed. Drop the trigger in, push the pins in place, and add the screws. Job done!
I would recommend putting a dab of blue Loctite 242 on the threads of the screws. You could also use Loctite 222 (purple) based on the smaller size of these screws.
Step Six: Safety Selector & Pistol Grip
Next up is the safety selector and pistol grip – these have to be installed at the same time.
The safety selector is installed from the left side of the receiver, just behind the trigger. It should slide in without too much trouble. If you find that it’s kind of binding, you can press your hammer (the one in your trigger group, not your trusty BFH) down toward the bottom of the receiver. That will actually put enough pressure on the back of the trigger, underneath the safety selector, so you can then slide it all the way through.
Now, switch to the grip. This one is a Magpul MOE, and the spring sits right in the top right corner of the grip.
There is a little hole in the receiver, right below that safety selector, where the spring goes. The safety detent goes in first and will hold your safety selector in place.
With the safety detent, make sure the pointed part goes towards the safety selector. The flat part goes down towards the grip. As you push the safety selector through the hole, you want to make sure that it is in the safe position or fire position. If you have it all the way over to the other side, it’s not going to click into the detent. When you push your grip up, make sure that you aren’t pinching the spring, causing binding or damage. Just slowly and squarely push the grip straight up onto the lower receiver.
Once you get the grip in place, take the bottom of the grip off and start installing the included set screw. This is a 3/16 inch hex. You could use a simple flathead. There is already a thread locker applied to the screw from Magpul. It is not Loctite. It’s actually a proprietary polymer something or other.
Step Seven: Takedown Pin, Buffer Tube, & Butter Retainer
The takedown pin will be installed in the back of the receiver. Make sure the grooves in the pin are facing the back of the rifle. Insert the pin into the hole just above the safety selector from the right side of the receiver. The takedown pin detent goes in next and will go straight into the back of the receiver, into the tiny hole in the bottom right.
Next is the takedown spring. With this spring and detent, you’ll install the buffer tube, the takedown pin, and the buffer retainer and spring all at the same time.
Don’t panic, it’s not that hard.
The buffer retainer spring goes inside the retainer and then into the top of the receiver.
The spring goes in first, followed by the retainer.
Next is the receiver extension (AKA buffer tube), castle nut, and receiver extension end plate. For the buffer tube, make sure the castle nut is all the way on and the receiver end plate is in front. The larger openings face the back of the rifle.
The slots in the castle nut will be used to tighten the castle nut down.
To install the receiver extension, make sure the castle nut and receiver end plate are screwed all the way onto the tube. You don’t have to tighten the castle nut down or anything, you just want to get it on the tube and out of the threads for the next step.
Next, carefully start screwing in the receiver extension (buffer tube) into the lower receiver. Don’t go crazy tightening this. Once the lip of the receiver extension touches the buffer retainer, use a punch to depress the spring, and simultaneously screw in the receiver extension.
The lip of the buffer tube is going to capture the buffer retainer. It is possible to over-tighten the receiver extension, so just take your time and focus on just getting the lip of it over the buffer retainer. Just watch the video again if this doesn’t make any sense.
Once you get the receiver extension in place, you want to make sure that your receiver end plate goes straight into the lower receiver and depresses the takedown spring squarely. If you try to push at a weird angle, the spring will bend and become inoperable. Very carefully compress your receiver end plate against your lower and screw down the castle nut.
Step Eight: Torque & Stake the Castle Nut
This is the Real Avid Master Armorers Wrench & Torque Wrench Combo that comes with the Real Avid Master Armorers Kit. There are lots of options for armorer’s wrenches available on the market, including Palmetto State Armory, Magpul, True Glow, and some Amazon options. I would not recommend the cheap ones from Amazon, but any armorer’s wrench should work.
This next step is one where you definitely want to throw your receiver in a vise. We are going to be applying about 40 foot pounds of torque here, so doing this without a vise can get pretty squirrely. The manual, TM 9-1005-319-23&P training manual, calls for between 38 to 42 foot pounds for the castle nut. I shoot for about 40, right in the middle, and that usually does the trick.
The manual also calls for Aero Shell 64 grease on the threads of the receiver extension and barrel nut. I don’t currently have any on hand, but the reason behind adding grease is to help prevent corrosion on the steel castle nut. If you get your rifle wet, something fairly common in the military, moisture can get trapped in the threads and cause some nasty rust issues down the road.
Castle Nut Torqe Spec 38-42 ft/lbs
How To Stake Your Castle Nut
Next, we are going to stake the castle nut. Staking means you’ll physically displace some of the metal from the receiver extension end plate into the grooves in the front of the castle nut. Again, now is definitely the time to use a bench vise if you have one. The more secure you can hold the lower, the less likely you are to cause damage.
To properly stake a castle nut, make sure to use a center punch or dedicated staking tool.
Very carefully hammer straight down to displace that metal from the plate into the castle nut. This will physically prevent it from rotating out of place unless you want to remove it in the future. Staking the castle nut is not permanent, and it really isn’t all that hard to do if you have a decent vise and punch.
Some people have suggested using red Loctite instead of staking, but –
DO NOT USE LOCTITE!
Especially, don’t use red 272 Loctite because it’s designed to be permanent, and the only way to remove the part is by heating it with a torch. If you use Loctite on your buffer tube and castle nut, there’s practically a zero percent chance you’ll be able to take the rifle apart again without breaking something.
The purpose of staking the castle nut is to prevent the castle nut from rotating and coming loose over time. Okay, so doesn’t Loctite do that too? Normally, yes. However, in this case, it won’t work as well as you think it should. This is primarily because the castle nut could be literally welded (you can’t weld steel to aluminum, but humor me) to the receiver extension, but that would not prevent the actual tube from rotating out of the receiver.
The receiver end plate has a large dimple that fits inside a recess in the lower receiver, which prevents the end plate from rotating. If you physically stake the end plate to the castle nut, you will ensure the tube can’t ever rotate accidentally. Long story short, the manual requires 38-42 ft/lbs of torque AND at least two stakes in the castle nut.
The secret to getting a perfect stake is just taking your time and only hitting the punch once before checking progress. If you start whaling away at the punch before it has a hole to start going into, it can slide around and really make a mess of your lower receiver.
Step Nine: Install The Magpul MOE Buttstock
Next up, we’re going to install the Magpul MOE buttstock. This particular stock from Magpul installs pretty easily.
There is a lever in the middle of the stock, which you depress, that pulls down a little plunger in the middle. To actually install it onto the receiver extension (the buffer tube), we have to depress that lever. We also have to pull down on the little bars on both sides. This can be done with a pair of pliers or your fingers. This would be another good use of Knipex pliers.
To install the stock, depress the handle, and grab the little bar with pliers. Pull straight down, and then slide the stock onto the buffer tube.
Step Ten: Install the Buffer and Buffer Spring
The last step is adding the buffer spring and buffer into the buffer tube.
The buffer goes into the spring, and then the spring is fed into the buffer tube. The buffer retainer will kind of click down to keep the buffer and spring in place. You should hear and see the buffer retainer click when you get it all the way in.
If you need an upper receiver for your new lower, here’s a few options to check out:
If you run into any issues or have a question or whatever, feel free to reach out to me. I don’t believe in talking down to new gun owners or people who may not be as versed in the AR ecosystem. I would be happy to help in any way that I can.