Unless you buy an assembled upper, you should know what the parts of an AR upper are and what they do. This will give you a more fundamental understanding of how the gun works, so you can deal with malfunctions and make repairs and upgrades as needed.
So, for instance, if you buy an AR15 upper build kit, or an AR upper parts kit, here’s what it should come with and what the parts do.
- Stripped upper: The stripped upper receiver is the part itself that receives all of the other upper parts, hence the name. An AR upper is typically made from aluminum and is considered either a billet upper, which is machined from a solid, extruded piece of aluminum, or a forged upper, which is formed by forging. Both can be excellent options, but forged uppers are considered slightly stronger.
- Handguard: The handguard encircles the barrel and protects it as well as the user’s hands. It also serves as one point of contact for the user to grip to control the gun. The handguard typically is either a tropical handguard, which has few to no attachment points, or else it is a rail system, such as a Picatinny (or “Pic”), KeyMod, or M-LOK rail system. These latter three have numerous slots and attachment points for adding shooting accessories such as sling mounts, swivels, lights, lasers, saddle mounts, and other attachments.
- Gas system: The gas system of an AR15 upper build kit consists of the gas block and tube, which are responsible for capturing gas from the barrel and using it to cycle the direct impingement action of the rifle. When gas expands in the barrel it gets siphoned off by the gas block, where it travels backward through the gas tube to the bolt carrier group’s gas key. Pressure builds here until the bolt carrier group unlocks and moves to the rear so that the action can be cycled.
- Barrel: The barrel is the part of the gun that traps gasses released when the propellant charge deflagrates, propelling the bullet through the bore. AR15 barrel lengths vary; in micro ARPs they can be as short as 4.5 or 5 inches, in SBRs they can vary between 10 and 16 inches, in carbines they tend to be 16 inches, and in rifles they can be 18, 20 or even 22 inches.
- Muzzle device: Most AR15 upper build kits come with a muzzle device that’s known as a flash hider. The flash hider obstructs the muzzle flash, helping to prevent temporary blindness to the operator, thereby preventing the sight picture from being obstructed. There are other muzzle devices, however, such as muzzle brakes, which reduce muzzle jump and felt recoil, as well as suppressors, which reduce the volume of the gun.
- Charging handle: The charging handle is the component that enables the action of the AR15 rifle to be manually cycled or manipulated, either for the purpose of charging the rifle or clearing jams. Most AR-style rifles are rear charging, but some are side charging, also known as side-chargers. Also, some AR15 upper build kits don’t come with charging handles, so make sure you check the listing before you buy or you might need to get one separately.
- Forward assist: The forward assist is a button or plunger-like AR part that is used to push the bolt carrier group closed if it has moved forward most of the way but failed to return fully to battery. This is another AR part that not all AR15 upper build kits come with, so make sure of the upper build kit’s inclusion before you buy.
- Dust cover/ejection port cover: The dust cover, also known as the ejection port cover, is a part that covers the ejection port, helping to prevent dust and other particulate matter from entering the ejection port when it is open. Like the forward assist and charging handle, this is an upper part that does not come with all build kits so double check before buying. However, the rifle will function perfectly well without this part, so be aware that it is not absolutely mission critical.
- Bolt carrier group: The bolt carrier group is the component that carries the bolt and thereby the firing pin, extractor, ejector, cam, and locking lugs. It serves sort of like the heart of the rifle and is responsible for loading the chamber, firing the cartridge, and then extracting and ejecting the spent shells. This is another part that does not always come with AR15 upper build kits, but it is one of the most vital AR parts of all. You cannot build a functioning rifle without an AR15 bolt carrier group.
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This short post covers most of the main AR15 upper parts that should come with either a build kit or an assembled upper. If you have questions, get in touch with us and we will be more than happy to help.