Buying or Building your First AR!  Here’s a Complete Guide to the Parts of an AR 15

The AR-15 is one of the most popular rifles in America and also one of the best defensive and dependable firearms, well of course, apart from being the best sporting rifle. This is F5 MFG’s series of blogs on ‘AR for beginners’ who are looking to buy or make an AR for the first time. Through this series of blogs, we will talk in detail about the parts, functioning, legalities, different versions, differences between these versions, and everything in between you should know about your AR.

This blog talks about the anatomy of an AR-15 or the different parts that constitute your AR-15 rifle. While you can buy a complete rifle from the gun store, you can also build this highly customizable firearm yourself from the ground up. To make this incredibly flexible, accurate, and easy-to-use firearm, you need to have a thorough understanding of its parts and the different accessories available to customize the firearm as per the configuration you like. Even when you go to the gun store to buy a factory-made AR, you need to have full knowledge of its parts and configuration to buy the best one as per your need. Let us dive into the detailed explanation of every part of an AR-15.

But before that, there are few things to note:

• AR is a platform to manufacture rifles and pistols (or handguns), developed by ArmaLite, which is where the rifle gets its name from. AR comes from the first two letters of ArmaLite and 15 denotes the 15th design of the AR series, hence the name AR15.
• Many firearm manufacturers now make their own version of an AR and its different parts.
• An AR can be a rifle or a pistol depending on its barrel length and shoulder stock.
• A standard configuration AR-15 famously sold in the US is a semi-automatic rifle, or a semi-auto carbine (rifle with a shortened barrel), or an AR15 pistol (with a short barrel less than 16” and without a stock).
• The semi-auto rifle or pistol means you can shoot only one round with one pull of the trigger, unlike a fully automatic rifle or pistol that keeps shooting rounds until the trigger is pressed or the magazine is empty.
• While there are other versions of an AR rifle, like the AR-10, AR-50, or AR-47, we will specifically talk about the AR-15 in this blog.

Let us now understand the different parts of a standard configuration of an AR-15.

Different parts of an AR-15

The AR-15 consists of an Upper Receiver and a Lower Receiver. Let us first talk about the parts in an upper receiver.

Upper Receiver of an AR15

The Parts in a Complete Upper Receiver of an AR15

The upper receiver consists of parts like a stripped upper (assembled upper with forward assist and ejection port/dust cover), bolt carrier group, charging handle, barrel, gas block, gas tube, handguard, and a muzzle device, as in the image above. The upper receiver is attached with the lower receiver to form a complete AR, ready to shoot. Let us see the different parts of a complete upper receiver.

• Stripped/Assembled Upper. An assembled upper comes with the forward assist and a dust cover. It goes on the bolt carrier group and the charging handle. On one side, it is attached to the barrel and the handguard, while on the other, with the stock. Check out F5MFG’s assembled upper with Picatinny rails and dust cover from Strike Industries. You can also check out F5MFG’s stripped upper without forward assist or dust cover. It comes dust cover ready but does not include one.

• Barrel. The barrel is the most important part of an AR. It is responsible for good accuracy and excellent velocity of your shots. The barrel should be more or equal to 16” because if the barrel length is less than 16”, your rifle will be called a ‘short-barreled rifle’ and you will be committing a felony if you build it without the NFA paperwork and the federal tax stamp. Check out our ultimate guide if you wish to apply for a tax stamp. Or, if you want a barrel less than 16”, the best you can do is buy or make an AR15 pistol, without a buttstock.

The other things you need to measure when selecting the barrel are its weight, handling, material and lining, rifling method, gas system, and chamber dimension. Apparently, button rifling or cold-hammer-forged are two of the best rifling methods to manufacture highly accurate and reliable barrels for your AR rifle, but these are also on the expensive and heavier side. Overall, make sure your barrel can tolerate aggressive firing if you make a decision to practice at least 100 rounds a week at the range.

• Bolt Carrier Group. The AR15 is a gas-operated semi-auto rifle that has a bolt carrier group that works on a direct impingement gas system. The bolt carrier group is responsible for the semi-automatic function of your rifle. It has a bolt, cam pin, firing pin, extractor, carrier key/gas key.

The BCG is responsible for loading the rounds in the chamber, firing them with each pull of the trigger, and finally ejecting the spent bullet casing from the chamber. The BCG does this by using the gases from the fired cartridge and directing it through the barrel towards the gas block, into the gas tube, and to the bolt carrier or the side assembly for every cycle to complete while ejecting the used casing and loading a new round. The direct impingement gas system makes the rifle more accurate, lighter, and less expensive to build. You can buy an assembled BCG or buy the parts and assemble them together. Check out F5 MFG’s bolt carrier group (BCG) for AR15. This assembled piece comes with a charging handle and is priced affordably at $139.

• Gas Block. It is the gas system that operates the cycling of an AR. The gas block maintains how much gas leaves the barrel and enters the gas tube and the receiver to push the BCG rearward for proper cycling. A standard factory-fitted gas block works fine for the factory-bought AR but when building the AR, you work with different weights of BCG or buffer. This is why you should go for a gas block that fulfills the purpose. You can go for a standard gas block that fits perfectly with the barrel or go for an adjustable gas block that can

• • Control the amount of gases entering the gas tube.
  • Use the exact force to push the BCG backward.
  • Control the gunk build-up on the inner walls of the gas system, upper receiver, and other parts.
  • Decrease recoil for even quicker cycling of the rifle.

The adjustable gas block might take more time to operate and clean but it would definitely make cleaning the firearm a less tiring task. You need to have a good know-how of the method of gas block mounting too. There are three mounting types for gas blocks – pinning (taper pins or straight pins), set screws, and clamp-on. Go for the one that solves your purpose and does not put much pressure on the barrel.

• Gas Tube. The gas tube is connected to the gas block and allows the gas to pass through to the bolt carrier group. You need to buy the gas tube as per the length of your barrel namely rifle-length, mid-length, carbine-length, and pistol-length.

• Charging Handle. The charging handle helps to chamber the first round to make your AR ready for use. The shooter does so by pulling the charging handle until the position where it can no longer be stretched and then letting it go with full force to load the first round in the chamber. The charging handle basically pulls the BCG rearward and strikes the hammer while making the BCG ready to pick a round and chamber it. It also helps when the AR malfunctions. You can do so by pulling the charging handle, releasing the faulty cartridge, and loading a new one. 
  

There are three types of charging handles. The type of charging handle you should get depends on your usage.

• • Standard Charging Handle. This is the most standardized cocking handle for an AR. It is a cheaper option when you want to get the job done without any fancy stuff.
  • Ambidextrous Charging Handle. Often referred to as a tactical charging handle, this type of charging handle is great for left-handed as well as right-handed shooters because it can be accessed from both sides of the firearm. 
    
  • Extended Charging Handle. This type of charging handle is great for shooters who wear gloves while shooting because it comes with an extended latch that is easy to grab and pull when wearing gloves or during night shooting.
  • Gas Buster Charging Handle. While using a suppressor, the gases blow back on the shooter’s face through the charging handle channel. A gas buster charging handle helps in mitigating or diverting the gases away from the shooter’s face.

• Forward-Assist. 

This feature is included in the ARs to make them more reliable. An AR works on a gas impingement system. These gases leave behind dirt, grime, and carbon deposit. If you do not clean the rifle after every use, the bolt carrier group may become dirty with carbon deposits and malfunction. It might not close properly and fail to load the round in the chamber. Another reason why the cartridge might not load is because of a bad round. A faulty spring is yet another reason why BCG fails to return to the battery. This is where forward assist can help you in pushing the bolt carrier group forward and placing it in its ready position while loading the round in the chamber. However, most of the shooters do not use it and find it as a useless feature on the AR. In the end, it comes to your personal preference whether you add the forward assist to your AR or not.

• Ejection Port Cover or Dust Cover.

Located on the right side of the AR, the ejection port cover ejects the used casing out of the firearm after the bullet is fired. The ejection port cover is always left open when you are using the firearm. Other times, when the firearm is not being used, this port is always closed to protect the bolt carrier group from dust. And we need not tell you what even a little bit of dust can do to your rifle performance. This is where dust cover helps you. You only need to keep the dust cover closed when not using the rifle so as to keep the BCG protected from dust.

• Handguard. As the name says, a handguard keeps your hands protected from the heat generated while continuous shooting. It works like a cover for the barrel and is also used to hold and support the rifle with a non-firing hand. There are two types of handguards you can go for; drop-in or floating handguards.
  • Drop-in handguards are usually cheap, easy to install, lightweight, and generally made with polymer. They come with a heat shield just below the polymer that is made with aluminum or steel to keep the polymer protected from the heat. But, the only drawback to this type of handguard is it can affect the accuracy of the rifle because of its design that goes to the forward part of the barrel with a handguard cap. They come equipped with mounting systems like Picatinny.
  • Floating handguards are mostly made with aluminum, are more costly than drop-in handguards, and do not extend till the forward of the barrel meaning they will never affect the accuracy of your AR. Floating handguards too come equipped with mounting systems like Picatinny, M-Lok, and Keymod to mount slings, sights, lasers, lights, bipods, forward grips, and other accessories.

Few things to consider before buying the best handguard for your AR are its mounting options, weight, accuracy, heat resistance, price, and ease of installation. Remember you will mount certain accessories on your AR for which you need the best mounting system and the accessories you buy will also need to fit on the type of mounting your handguard has. The accessories will also increase the weight of the firearm so make sure you buy something you are comfortable with, probably a lighter one. The handguard should also be easy to install and uninstall as you might want to clean your AR as and when you use it. Choose the handguard accordingly.

• Muzzle Devices. There are many kinds of muzzle devices like compensators, suppressors, flash hiders, and muzzle brakes to tame recoil, prevent muzzle climb/barrel rise, cool and disperse the burning gases, and controlling the sound of the gunshot.
  • Compensators. Every shot fired leads to a muzzle rise or barrel rise from recoil. This impacts the accuracy and speed of the firearm to make itself ready for the follow-up shot. Compensators help compensate for the muzzle rise, meaning they divert the gases produced during firing to the vents on the sides and upward and lets them out. This way compensators help control muzzle rise which in turn improves the accuracy of the shots. This also allows the shooter to take quick follow-up shots.
  • Muzzle brake. The muzzle brake helps tame recoil while continuous or rapid firing by venting the gases out from the sides of the muzzle brake. Both compensator and muzzle brake work alike by venting the gases out of the barrel, the difference being compensators help control muzzle rise and muzzle brake helps tame recoil. Muzzle brakes, too make the firearm more accurate and quicker to fire the follow-up round.
  • Flash Hiders. When the projectile exits the barrel, the unspent gunpowder, and high-temperature gases leave behind a trail of combustion that comes out of the barrel. Flash hider works by suppressing this combustion giving a clear vision to the shooter. Flash hiders are a helpful accessory especially in low light or no light conditions.
  • Suppressors. Officially called silencers, suppressors help by reducing the sound of the gunshot. They do this by slowing the release of the propellant gases and transforming the sound of the gunshot into heat.

There are many styles and designs for every type of muzzle device for an AR. Choose as per your budget, the size of the muzzle, and your specific needs.

The Parts in a Complete Lower Receiver of an AR15

The lower receiver includes stripped lower, lower parts kit, trigger, buffer kit, magazine, buttstock, pistol grip, and all other necessary parts like safety selector, bolt catch, and foregrip. Like the upper receiver, you have the option to buy a complete lower receiver and throw it on the upper receiver to complete your AR. Let us talk about different lower receiver parts.

• Stripped Lower.

The lower receiver comes with the fire control group, which includes trigger, magazine eject, safety, and bolt release. There are two ways you can obtain a lower receiver.

• • Buy a complete stripped lower.
  • Build from an 80% lower receiver.

The stripped lower receiver is legally considered the firearm itself and regulated by the ATF with a serial number. Why? This is because the lower receiver of the firearm can be easily and readily converted to expel the projectile. You will need to buy the stripped lower and have it shipped to the FFL licensee. Only after undergoing a thorough background check can you have the lower receiver shipped to you. We will leave the legalities of a lower receiver to another blog. You can also buy an 80% lower receiver and complete it yourself. Buying this won’t require an FFL license as it is not considered a firearm and is manufactured at home for personal use. 80% receivers require a drill press or precision jig to complete them. Check our F5 MFG’s 80% lower receiver along with the machining jig to complete your 80% lower receiver from F5.

AR 15 works with different calibers of ammo, the most common being .223/5.56 x 45. It does not depend on the lower receiver what caliber ammo you use. Just mount a different upper and you are good to use different calibers.

• Lower Parts Kit. It will have all the parts that will help you to complete your lower receiver like a bolt catch – plunger, spring, roll pin, the hammer – pin and spring, takedown detents and springs, disconnector and disconnector spring, pivot pins and detents, a safety selector – detents and detent spring, the mag catch and button, and other hardware. Buy a quality lower parts kit from a renowned manufacturer so that you can always rely on your weapon.

• Trigger.

The trigger is one of the most important parts of a rifle because this part is the one that helps shoot your AR and become a pro shooter over time. The trigger group consists of a trigger, disconnector, hook, hammer, sear, pins, and springs. You can buy the trigger in the lower parts kit or separately as the trigger group. Always buy a trigger group as per your requirement. Nonetheless, it should be reliable, dependable, and accurate. An accurate rifle should have a smooth trigger pull, neither too light nor too heavy. A trigger with a heavy pull weight won’t be accurate and faster as your hands would shake when you try to exert more pressure on the trigger, ultimately missing the target while, a lighter trigger stands a chance of negligent firing.

Majorly, there are two kinds of triggers – single-stage triggers and two-stage triggers. All the rifle triggers fall under either of these two categories but with different weights, styles, shapes, and materials.

• • Single-Stage Trigger. This is the standard mil-spec trigger that you get in an AR15 when you buy it as a complete rifle. Single-stage trigger fires as and when you pull the trigger. In other words, it’s just a single pull until you reach a specific pressure where the hammer releases and hits the firing pin, and the round is fired. A new shooter should go for the single-stage trigger until they become an expert to use the two-stage trigger.
  • Two-Stage Trigger. A two-stage trigger comes with a custom disconnector and two hooks on the hammer in spite of one hook as in the case of a single-stage trigger. This means the hammer hooks at two places with the disconnector before hitting the firing pin. A two-stage trigger uses a little force until it reaches a wall and then some more pressure would complete the shot. 
    
  • Binary Trigger. When you want to experience a somewhat full-auto fire on a semi-auto rifle, you can get a binary trigger for your AR. Binary trigger shots the first round on the pull of the trigger and another when releasing it. Binary triggers have a higher rate of firing. Binary triggers need a lot of practice before you can use them. There are some state restrictions on buying and using a binary trigger. Check for your state laws before adding one to your AR 15.
  • Adjustable Trigger. These are the ones on which you can adjust the trigger pull weight by adjusting the take. The minimum weight of your trigger pull should be 3-4 lbs, it won’t be too light or too heavy.
  • Drop-in Trigger. Drop-in triggers come pre-assembled in a cassette type housing and need to be dropped in the lower receiver, hence the name ‘drop-in.’ They do not create any take-ups, stacking issues, over-travel, or creep. They are easy to install and come in as a single-stage, two-stage, binary, and adjustable trigger. The adjustable ‘drop-in’ trigger would only allow you to adjust to different preset trigger weights.

• Buffer Tube/Buffer. Also known as the receiver extension, the buffer tube is a metal tube that houses the buffer and the buffer spring. Buffer absorbs the recoil when the round is fired. Buffer tube goes from the receiver to the stock to work as an attachment system for the stock. Buffer also helps the bolt move back and forth to eject the used cartridge and load a new one. The bolt moves back with the gas from firing and goes back forward by the action of the buffer. Buffers come in different weights, sizes, and housings. The weight of the buffer is critical to the smooth functioning of the bolt carrier group. The different weights for a buffer are
  

• • • Carbine – 3 oz
    • Heavy (H) – 3.8 oz
    • H2 – 4.6 oz – 4.7 oz
    • H3 – 5 oz to 5.4 oz
    • HSS – 6.5 oz

Get the one that’s heavy, but not too much, to allow your rifle to take a full cycle without any error. If your rifle is able to lock with an empty magazine, it means it has a good buffer weight. The best way to find a suitable buffer is by loading a single round in the mag and checking if it locks many times in a row. Also, make sure you go with the exact size that goes for your AR 15 rifle.

• Buttstock. Also called the shoulder stock, the buttstock is the part that is attached to the firing mechanism at the end of the rifle. The stock rests on the shooter’s shoulder for support to the rifle and accuracy in shots. Shouldering the rifle from the stock also helps to control muzzle rise by transmitting the recoil to the shooter’s body, well then, of course, there are many other parts to control muzzle rise. There are two kinds of buttstocks, fixed and adjustable stocks.
  

• • Fixed Stock. As the name says, fixed stocks are permanently fixed to the rifle unless and until you change them or field strip the rifle. Fixed stocks are rigid and sturdy and offer good accuracy and stability to the weapon because you become used to the same sized weapon every time you use it, in the end making you adjust to the stock’s specs.
  • Adjustable Stock. Adjustable stocks can be adjusted as per the length of pull you prefer. They adjust to 6-7 different positions depending on the brand you use. This makes the weapon more versatile to use and easy to carry.

Stocks come in different enhanced shapes and sturdy materials along with features like a replaceable buttpad, rounded cheek weld, QD sling socket, and more. It totally depends on your personal preference what kind of stock you prefer on your AR. The market gives you innumerable options to choose from. Get the one best suited to your needs and preferences.

• Magazine. A magazine is the part that holds the cartridges. The magazine should be selected as per the firearm manufacturer, model, caliber, and capacity. This means a magazine which is compatible with your rifle will accept the cartridge with a caliber that the rifle can chamber, that fits with your firearm’s brand and its model. You should also consider if the mag is easy to feed, disassembles easily, and works flawlessly. There are different capacity magazines but civilians usually go for 20 rounds, 30 rounds, or large capacity magazines with 50 rounds and 100 rounds. It, however, depends on your state and local laws if you can use high-capacity magazines or not. You can either buy a

• • Polymer Magazines. They are lightweight, reliable, heat-resistant, do not rust, and work in almost every weather condition. Some polymer magazines also come with a transparent window which allows you to see how many rounds you are left with. Polymer magazines generally do not have deformed feed lips and work well unless and until they are broken, they become completely useless.
  • Aluminum or Metal Magazine. They are highly durable with their metal feed lips that work without any error. However, make sure you check the feed lips of any magazine you buy to be sure of any deformity. They are reliable, robust, lightweight, and can resist heat when coated with a heat-resistant material.

The magazine of an AR 15 fits with a caliber according to the make and model of the rifle. Usually, the AR 15 mags are chambered for .223 Remington or 5.56 NATO. Check out F5 MFG’s 5.56/.223/.300 AR-15 50 rounds drum magazine. It’s a robust, reliable, and a high performance magazine.

• Grip. Yes of course, you hold your rifle with the grip. A perfect grip ensures rifle’s accuracy, better management of recoil, and a good shooting experience. There are two kinds of grips on an AR 15 rifle.

• • Pistol Grip. Pistol grip is the one on the lower receiver. Your trigger hand holds the pistol grip which is why it needs to be the perfect one that you are comfortable with. There is a huge aftermarket for grips, find the best one that feels comfortable in your hand and gives you the best hold.
  • Foregrip. Apart from holding the rifle with the pistol grip, a shooter needs to keep a firm hold of the long barrel of the rifle with their other hand. Yes, that can be done with the handguard. But if you can legally use the foregrip on a rifle, then why not? The foregrip gives a much better control on the rifle and recoil. Well, because two are always better than one, right? Check out the vertical foregrip from F5 MFG that allows for the ambidextrous use, picatinny mounting deck, and storage compartment.

Those are the parts that make up your AR 15, buy the rifle as a complete gun or make one at home. F5 MFG offers a wide range of AR 15 parts and accessories that help you make a complete rifle from ground up. Stay tuned for our next blog where we discuss the functioning of this amazing rifle.