If you’re new to the AR platform you might be super confused about what all of the parts do and what their names are.
Never fear, that’s why we’re here!
From the muzzle device to the buttstock, we have every part listed and we’ll tell you what they do!
Upper Receiver Group
The receiver itself is a simple part and doesn’t play much of a role in the durability or reliability of a rifle. As long as it is within standard specs, that’s all that matters. The upper receiver holds many other critical parts such as the bolt carrier group, AR scope, charging handle, forward assist, as well as the barrel and handguard attaching to the front of the receiver.
Barrel & Barrel Nut
The barrel is the most important part for accuracy and precision. Every part being of high quality is nice, but the barrel is the place to spend the big bucks if you want a precision rifle. That said, even fairly low-shelf barrels can be very accurate depending on your goals.
Barrels come in a wide range of lengths, twists, and profiles. For all of the info on that, take a look at The Best AR Barrels: Length, Material, and More.
The barrel nut is a large screw-on nut that keeps the barrel connected to the upper receiver. Simple, durable, solid.
Gas Block & Gas Tube
The gas block attaches to the barrel near the muzzle above a gas port that is drilled into the barrel. This allows gas to escape from the barrel into the gas block, down the gas tube (attached to the gas block), and into the bolt carrier group to cycle the rifle.
Gas blocks and tubes are ultra-simple parts that almost never fail for any reason. If you want to get fancy, an adjustable gas block allows you to regulate how much gas is allowed through the block and into the bolt carrier group. Less gas means less felt recoil but also less strength to cycle the rifle.
On the other end of the complexity spectrum is the Front Sight Block that acts as both a front iron sight and a gas block. These are less popular these days since they prevent a barrel from being free-floating (the barrel does not connect or interact with anything other than the gas block and barrel nut/receiver) but they are a classic option that guarantees a front sight that will never fail you.
Something to note is that your gas tube can be of many sizes. Generally speaking, longer is better. Rifle > mid-length > carbine > pistol.
Longer gas tubes mean less gas and pressure into the system, this makes for a softer recoiling firearm and less wear on internal parts.
However, your AR-15 gas tube is limited to what the barrel requires. I always recommend getting the longest gas system that your barrel can use, but that isn’t always possible.
There is such a thing as a gas system that is too long, but you won’t need to worry about that. The science of how to gas an AR-15 has been figured out for a long time and manufacturers know how much barrel is needed for each gas system to work correctly.
In my book, handguards don’t get the respect they deserve. Connecting to the upper receiver and wrapping themselves around the barrel a good handguard not only gives you a place to put your hands but also protects you from heat and catastrophic failures. If something goes boom that shouldn't, a good handguard might be the last line of defense between you and some unwanted shrapnel.
Not only that but a good AR-15 handguard will also give you room and mounting points for lights, grips, sights, and more.
Take a look at our article on Picatinny, M-LOK, and KeyMod for more info!
Ranging from flash hiders to brakes to compensators to suppressors, a muzzle device attaches to the end of the barrel and in some way uses the escaping gases to produce an effect. What effect depends on the device.
Flash hiders direct the gasses so that the muzzle flash is sent away from the shooter to help preserve your vision in low-light.
Compensators direct gases upwards to help force the rifle down and reduce muzzle flip.
Brakes send gases backward and/or to the side to help reduce felt recoil. Brakes and compensators are often combined into one device.
Suppressors are large cans that give the escaping gas a contained volume of space to expand and cool in before exiting the suppressor. By allowing the gas to cool it radically reduces the sound of a gunshot.
Bolt Carrier Group: Bolt Carrier, Bolt, & Firing Pin
The bolt carrier group includes everything that the BCG needs to function such as the carrier itself, the bolt, firing pin, cam pin, and a retaining pin. This is the engine of your AR-15 and is the most important part for long term durability and reliability.
Generally, a BCG is bought as a complete unit and includes everything you need. However, if you’re feeling fancy you can get the carriers and bolts separately to mix and match some interesting features offered by some other manufacturers.
Depending on who you ask the forward assist is either a critical part or completely useless. Standard AR-15 upper receivers will have a place for a forward assist on the side of the receiver that allows the forward assist to be pushed forward and into the side of a BCG. Nearly all BCGs have ratcheted teeth on the side for the forward assist to act on. Pushing for forward assist forward forces the BCG forward and into battery.
Upper receivers without a place for a forward assist to be installed are often called “slick side” receivers.
I will leave the debate on the forward assist’s merits to be argued in the comments, but I’ll go first saying I don’t like them and most of my rifles are slick side.
Another part that doesn’t really get the respect it should is the charging handle. Attaching to the front end of the BCG and extending out the rear of the upper receiver, is how you manually cycle the rifle in a normal AR-15.
A normal charging handle is good enough, but upgraded models will often feel smoother and make for a nicer pull, provide ambidextrous handles, or include cuts or rises to redirect excessive gasses from the shooter -- these are commonly useful if you’re running a suppressor, but generally not needed otherwise.
Lower Receiver Group
The lower receiver, much like the upper receiver, is a very simple and oddly unimportant part of the AR-15. While it holds everything together and features can be built into it, it doesn’t really do anything that adds or takes away from the overall durability and reliability of the rifle.
Often, the main differences between AR-15 lowers are simply the markings on the outside and the aesthetics of the design.
However, there has been a major push in the last few years for ambidextrous rifles. Since the lower receiver houses almost all of the controls, it is the most difficult part to make truly ambidextrous.
To be a true ambidextrous a lower needs an ambidextrous safety, magazine release, and bolt catch. The safety and magazine release can be retrofitted onto any standard mil-spec lower with ease, but the bolt catch is much harder.
Adding an ambidextrous bolt catch normally requires re-milling the lower. If you’re interested in a true ambidextrous lower, make sure you pick one that comes pre-designed with a bolt catch in mind.
Fire Control Group: Trigger, Hammer, Disconnector
Generally, these will just be called “triggers” although that is technically just one part of the fire control group. But to make life easy, it’s a trigger.
If we want to be technical -- the trigger is the part that hangs out of the lower and you pull to make the gun go bang. The disconnector sits on top of the trigger and prevents your AR-15 from dumping every round on the first trigger pull. The hammer connects to both the trigger and the disconnector and is what actually smacks the firing pin to set off a cartridge.
Any mil-spec trigger is good enough to get by on, but there are lots of aftermarket triggers that really clean up the pull and break on an AR-15.
If you want a precision rifle, a great trigger is the second most important part to pay attention to.
You can also do really fun things like binary triggers that fire a round on the pullback and on the release forward and radically increase the fire rate!
It’s a tube that holds the buffer. That’s it. That’s what it does. Add something like the Law Tactical Folder and you can make it… fold. Otherwise, a buffer tube is a buffer tube.
Okay, really they come in two major flavors -- carbine and rifle. Carbine tubes are normally adjustable and are designed for carbine stocks (NOT gas systems, carbine stocks!) while rifle tubes are designed for things like an A2 stock or any other stock that uses the rifle style.
Buffer Spring & Buffer Weight
The spring and weight inside the buffer are what dampens the recoil of the BCG and send the BCG back into the upper after every shot.
If you’re interested in tuning your rifle so that it is reliable but has the least about of recoil possible, changing the weight of the buffer and the strength of the spring are great ways to do that.
Going too heavy can cause the rifle to short stroke. Too light will cause excessive wear, more recoil, and induce strange malfunctions.
Weights and springs come in lots of flavors such as carbine tubes or rifle tubes. Make sure to match the right ones with the type of tube and stock you’re using.
The big thing that rests on your shoulder! From small carbine stocks to large precision rifle stocks, a good buttstock can make or break how a rifle feels in your hands.
Don’t be scared to play around with your options and find what fits you best.
It’s what you hold on to. You didn’t see that coming, did you? Yes, you did. Grips come in LOTs of flavors and are as personal as glasses. The standard milspec A2 grip isn’t bad, but there are lots of better designs depending on what you need.
I like a grip that is very grippy, so lots of aggressive stippling. I also want ones that are a bit larger than normal since I have big hands.
If you’re a pistol shooter, think about what you like in a pistol grip and look for an AR grip that matches those characteristics.
Safety on = rifle no go pew, safety off = rifle go pew. I like ambidextrous ones, but standard ones are fine too.
Pins that hold the complete upper together with the complete lower. Just get milspec ones, don’t be one of those weird people who spend $60+ on titanium pins or something else silly like that.
Technically the bolt release both releases and catches the bolt. I'm not sure why they are just called releases.
Either way, when your BCG goes and there isn’t any ammo left to pick up, the bolt release stops the bolt from moving forward so you can reload easily. Press the bolt release once you’re loaded up and the BCG will fly forward and chamber a new round.
There are sizes and styles out there for you to pick from, but I like just a normal milspec one.
You can invest in a fancy one, but I’ve never seen them do anything that a cheap one doesn’t do.
If you want to get an AR-15 magazine out, you’ll need one. For that matter, if you want a magazine to stay in -- you’ll still need one.
Unless your magazine release is ambidextrous, there is nothing that a fancy one does differently than a normal one.
I’m a huge fan of ambidextrous magazine releases and they are super easy to install.
And there you have it -- all of the parts of an AR-15!
I hope that helped you get introduced to America’s most popular sporting rifle. If you have questions, let me know in the comments!
[We'd like to extend a huge thank you to David Lane for his hard work on this article. Leave a comment below and check out our huge selection of AR-15 rifles, AR-15 uppers, AR-15 parts, and more all made in the USA!]