How to Build an AR-15 [Complete Parts Guide]
This is a guide on how to build an AR-15 is just a parts list and information about each part. You can find an assembly guide here.
Building an AR-15 is a fun experience and it helps you to really understand your gun. However, there are some pros and cons to the whole building experience that you should understand before you start.
Pros of Building Your Own Rife
- You can really understand your rife and how it works.
- You can spread the expense out over time.
- Can save you money.
- Complete customization.
Cons of Building Your Own Rife
- No warranty
- You can mess it up if you don’t know what you are doing. The gun may not cycle or fire properly.
- Can get expensive quick.
- You need specific tools.
What to look for when choosing AR-15 parts.
Caliber
When building an AR-15 you get to decide a caliber. This choice will determine a lot of the parts and options that you have moving forward.
The most common caliber for an AR-15 rifle is 5.56 NATO; however, depending on your intended use, there may be a better option for you.
Check out my complete caliber guide before you make this decision.
Mil-Spec
Mil-Spec stands for Military Specification, and just means that the piece meets a standard size and quality requirement set by the US military.
Now this does not mean that Mil-Spec is highest rating a piece can receive. However, if you are looking for pieces to fit properly, and function properly, the Mil-Spec rating a great minimum bar.
Mil-Spec is also great because it can give you peace of mind that things will fit together. Fancy new technology can be great, but if it doesn’t attach properly to the other pieces of your kit, then what good does it really do?
Before you mod out your kit and get over fancy. Ensuring that your gun fires properly should be your primary concern. If you are going to deviate from Mil-Spec, make sure that the adjacent pieces can accommodate the deviations.
Registering your Gun
As far as registering your AR-15, there is only 1 piece on a standard AR-15 that needs to be registered, and that is the lower receiver. This is the only serialized piece of a standard AR-15. In order to get this piece, you will need to pass a standard gun background check when you buy, and must be distributed by a registered FFL.
When I built my latest AR-15 there were two additional reasons that I had to register my gun. These two ATF registrations are fairly common.
Short Barreled Rifle (SBR) Tax Stamp Application is needed for any gun that has or originally had a buttstock, and has a barrel under 16”. There are braces that are not included in this classification.
An SBR tax stamp costs $200 and you are required to fill out and file ATF Form 1 with the ATF.
Another gun accessory that has a serial number that needs to be registered is a suppressor. If you would like to purchase a suppressor it will require another $200 tax stamp and you will need to fill out an ATF Form 4.
The easiest and most efficient way to purchase a suppressor and make sure that all your paperwork is in order is to do it through SilencerShop.
SilencerShop has easy to use kiosks at gun stores around the nation that help take some of the guesswork out of these forms. It gives you someone to call in case you need support.
Necessary Tools for Installation
The last thing you want to do with high performance piece of equipment is skimp out on installation. Cutting corners on your tools can lead to broken pins, stripped nuts, and more.
It may cost you an extra few hundred dollars to get the proper tools to build a gun, but it is important.
Bench mounted vice grip, BEV Block, and Reaction Rod are needed to keep your gun sturdy while building.
A Torque Wrench is needed if you want to tighten things to spec. I recommend doing this, because this will guarantee a tight fit without stripping any of your new (and probably expensive) new pieces.
An Armorers Wrench will help you to to attach specific pieces onto your rifle. Not 100% needed, you can muscle or rig up a standard wrench for some of this, but it is worth the investment.
A good Punch Kit is absolutely necessary and something that I wouldn’t go cheap on. You will need this to manipulate roll pins. In addition to the punch kit, Roll Pin Holders make the whole process much easier. They are not completely necessary, but make your life a lot easier.
Upper Receiver
Here are all the parts for the Upper Receiver.
- Stripped Upper Receiver
- Bolt Carrier Group
- Charging Handle
- Handguard
- Gas Tube
- Gas Block
- Dust Cover
- Barrel
- Muzzle Break
Stripped Upper Receiver
This is the starting point of your upper receiver. This is a piece that you can actually save some money on. Make sure that you are getting an upper receiver from a reputable and tested company. If you are spending more on your upper receiver, it is usually because of fancy designs, not actual functional upgrades.
Bolt Carrier Group (BCG)
One of the most important pieces of your rifle. If you try to think about what parts of your rifle are going to be experience the most wear and tear, it is going to be the the pieces that come in direct contact with each round, and the pieces that cycle with each fire. The bolt carrier group fits in both these categories.
When choosing which pieces of your AR-15 your can save money on, and which ones you should focus on quality, the BCG should be a quality piece. There are lots of quality BCG options on the market.
When choosing a BCG it is important that you find one that has been High-Pressure Tested and Magnetic Particle Inspected.
Charging Handle
An easy piece to change out on any AR-15 rifle that you own. Most charging handles do not effect the overall performance of the rifle, but usually can enhance the user experience by making things easier to operate. There are a couple things to look for when looking for the best charging handle.
Two common upgrades for your charging handle are ambidextrous charging handles and gas busters. These upgrades give you more surface area to to have fast and easy access. The gas buster helps to prevent gas from being blown back into your face as the gun cycles.
Handguard
When building your AR-15, picking the right handguard is is important because it can limit the modifications that you can add later. Not only that, but it also effect the ergonomics of your rifle. Ergonomics is one of the most important factors of your rife, because a correct shooting position has more of an effect on accuracy than anything else.
When choosing the best handguard for your build make sure that you choose the correct mounting option. The most common mounting methods today are M-LOK, Keymod, and Picatinny Rail.
Gas Tube
The gas tube is the part of the gun that sends expanding gas from the explosion in your barrel back into your BCG in order to cycle your gun.
When purchasing your gas tube, the most important factor is length and this will depend on your barrel and where the gas port hole is located on your barrel.
There are 4 different gas tube lengths: Pistol Length, Carbine Length, Mid Length, and Rifle Length. Make sure that you buy the appropriate gas tube for your barrel.
The different lengths effect the amount of recoil energy that is used to cycle your BCG correctly.
Gas Block
The gas block is used to trap the gas before sending it through the gas tube and back into your upper receiver. The amount of gas that is captured is dependent on the length of your gas tube, unless you have an adjustable gas block.
An Adjustable Gas Block gives you a little more control over how much gas is forced through your system. If you are going to be shooting suppressed or subsonic, having an adjustable gas block will allow you to easily optimize the flow of gas through your system to optimize cycling.
Dust Cover
Dust covers are a pretty small piece of equipment with not a lot of innovation over the years. It is a spring loaded piece of metal that covers up your ejection port when the rifle is not firing.
There is some discussion as to the necessity of dust covers; however, my opinion is that they are better than nothing, and they do protect from larger rocks and obstructions getting into your upper receiver.
Barrel
Probably the second most important piece of equipment on your upper receiver, behind the BCG. Every single round that you fire has to go through your barrel, and it will have an effect on your entire shooting experience.
The most important factors when choosing a barrel are length, material, caliber, and twist rate.
Length of your barrel will determine if you need an SBR stamp, which could make your initial gun application a little more difficult. There are many advantage and disadvantages for barrel lengths.
Your caliber choice will also play a factor in your length decision. Check out a complete caliber guide here.
Most people are not going to be able to outshoot their barrel. Meaning, if you are new to shooting, your barrel is going to be more accurate than you. However, if you are getting into precision shooting, choosing the correct barrel will have a bigger impact on your shooting.
Muzzle Break
Don’t get caught up on muzzle breaks. There are lots of fancy muzzle breaks for you rifle that can mildly reduce recoil or flash. However, when building your AR-15, there are other parts of your gun that will have a much bigger impact on your shooting performance.
In my opinion, the big exception to spending extra money on a muzzle break would be for a threaded mount for your suppressor. Most suppressors will have a branded muzzle break that will allow you to quickly detach your suppressor and still fire your weapon.
Lower Receiver
Here are all the parts for the Lower Receiver.
- Stripped Lower Receiver
- Lower Parts Kit
- Safety Selector, Selector Spring and Detent
- Trigger Guard and Roll Pin
- Magazine Catch, Spring and Button
- Front Pivot Pin
- Rear Take Down Pin
- Two Takedown / Pivot Pin Detents
- Two Takedown / Pivot Pin Detent Springs
- Bolt Catch, Plunger, Spring and Roll Pin
- Buffer Retainer Pin and Spring
- Trigger Assembly Kit
- Buffer Tube Assembly
- Buffer Tube
- Buffer Spring
- Buffer
- Castle Nut
- Latch Plate
- Buffer Retainer Detent
- Buffer Retainer Detent Spring
- Stock
- Grip
- Magazine
Stripped Lower Receiver
This is the starting point for your lower receiver. This is also the only serialized piece of a standard AR-15. There are lots of options for your lower receiver, but this is a piece where you can save some money, without sacrificing quality or performance.
Lower Parts Kit (LPK)
For you lower parts kit, there are lots of options, but make sure that you are getting a Mil-Spec kit. That way all of your pins and springs will fit.
- Safety Selector, Selector Spring and Detent
- Trigger Guard and Roll Pin
- Magazine Catch, Spring and Button
- Front Pivot Pin
- Rear Take Down Pin
- Two Takedown / Pivot Pin Detents
- Two Takedown / Pivot Pin Detent Springs
- Bolt Catch, Plunger, Spring and Roll Pin
- Buffer Retainer Pin and Spring
Some LPKs will come with grips and triggers. However, I recommend getting an upgraded trigger and not running a Mil-Spec trigger.
A Mil-Spec LPK will include everything you need, but there are a few pieces that can be upgraded for convenience. One piece I recommend upgrading is your bolt catch to a maritime bolt catch. This is a nice upgrade because there is more surface area to drop the catch.
Trigger Assembly Kit
Your trigger may come with your LPK; however, upgrading your trigger will give you greater control over your AR-15.
There are lots of options with triggers and it mainly comes to preference. The best way to find out what kind of trigger you like is to try and shoot a few first. You may not know whether you want a single stage or 2 stage trigger. The other factor will be pull weight.
Buying the best trigger depends primarily on what type of trigger you enjoy shooting.
Buffer Tube Assembly
The buffer tube has two purposes. First, it absorbs some of the recoil from the gas system. Second it acts as a mounting plate for your stock.
- Buffer Tube
- Buffer
- Buffer Spring
- Castle Nut
- Latch Plate
- Buffer Retainer Detent
- Buffer Retainer Detent Spring
There are different buffer weights depending on what length gas system you are using and the length of your barrel. So make sure that if you are using a Carbine Gas System, that you are also using a Buffer Kit designed for a Carbine system.
Stock
There are a lot of stock options out there. You may be getting a fixed precision buttstock, a folding brace, or adjustable stock. Choosing a stock comes down to comfort and usage.
If you are going to be doing bench rest shooting, having a heavier, sturdier stock may help with precision. However, if you are building a gun to carry and shoot in a variety of positions, something lightweight and adjustable may be the best option.
Make sure that whatever you get is comfortable. Ergonomics and comfort have a significant impact on your shooting. Having proper ergonomics will effect your trigger pull which in-turn will effect your accuracy.
Grip
Similar to your stock, the comfort and ergonomics of your grip will have a significant effect on your overall shooting performance. The best grip for you will be the one that is more comfortable for you hold.
Magazine
When it comes to magazines, I would say err on the side of getting too many. You never know when you are going to need few extra mags.
It’s also nice to go to the range with some magazines already loaded so you can make the most out of your time training.
Make sure that you are rotating your ammo thru your magazines on a regular basis, this won’t be hard if you are training regularly.
Other Parts
Here are some other parts for your AR-15.
Optics
Optics will probably have a greater influence over your shooting performance, than any other piece of equipment. Buying poor optics that can’t hold zero is just a waste of money. You are better off just getting iron sights at that point.
If you are going to be spending money on a red dot or scope, I recommend budgeting a little bit extra. Finding a reliable optic is important, and while you are saving up for that, you can always use iron sights.
Supressor
After shooting suppressed, it is hard to imagine what life was like before. It just feels wrong to not shoot suppressed. It does take a little bit of time to get your tax stamp get through that whole process; however, it is well worth the wait.
The nice thing about building an AR-15 is that you can do it in stages. You do not need to buy everything all at once, and a suppressor can be purchased at any time. If you are planning on going suppressed, make sure that you get the correct muzzle break for you gun early.
Check out this list of best suppressors.
Flashlight
Depending on your intended use, a flashlight is a great addition to your AR-15. If you are building a target precision rifle or a hunting rifle, a flashlight may not be necessary.
However, if you are building a home defense weapon, then having the tactical advantage that comes with extra light is important.
If this is going to be a life or death weapon, you should strive to give yourself every tactical advantage possible. Light and the ability to see where you are shooting, could be the difference between safety or harming the wrong person.
When mounting your light, make sure that the placement allows you to turn the light on and off easily. Not only that but when looking for the best AR-15 light, make sure that you find one that mounts securely on the rail that you purchased.
Rail Accessories
You can add almost anything to your rail. But you shouldn’t. Over customizing is a problem that a lot of new AR-15 builds have. Make sure that everything that you add is tactical and has a use. One rail accessory that I love is Railscales.
Whatever you do to your rail, make sure that you don’t over do it.
Sumary
Building an AR-15 is a lot of fun. But it also can be difficult and not always better than a rifle out of the box.
If you are looking for ease and reliability, take a look at my best AR-15 guide.
Personally, I loved building my own rifle, I’m building another right now, and plan to do more builds in the future.
