Let's start our breakdown of the AR-15 upper components with the bolt carrier group. It can also be called the BCG for short. The bolt carrier group is responsible for performing the semiautomatic fire when the trigger is pulled with a series of steps in this order:

• Allowing the firing pin to strike the primer on the chambered round
• Grabbing and ejecting the spent shell casing from the fired round
• Re-cocking the hammer in the lower receiver for the next round
• Grabbing a new round from the magazine and chambering it.

As you can see there's a lot of things going on in one continuous motion. In order for that to be completed, there are a series of components inside the bolt carrier group: the firing pin, the bolt, the cam pin, extractor, and gas key. For most of us, the bolt carrier group will come included when we purchase our AR-15. However, there are a myriad of upgrades you can perform on any of these basic parts in order to get the results you're looking for. And that is a basic overall summary of what the bolt carrier group does in the AR-15 upper.

Noveske 5.56 Bolt Carrier Group. Image from Wing Tactical.

Radian Raptor Ambidextrous Charging Handle. Image from Radian Weapons.

The next part of the AR-15 upper that we're going to look at is right on top of the bolt carrier group and it's called the charging handle.

Now, the charging handle is the part that pulls your bolt carrier group to the rear when you need to chamber a round or to clear a malfunction. If a round doesn't fire as it should, you can simply pull on this charging handle to release the faulty shell and reload a new one. A charging handle will also let you load the first round of a new magazine if the bolt is closed. When you fire the AR-15, the charging handle remains stationary. Just like the bolt carrier group, there are a lot of different options you can pick from to upgrade your charging handle on the AR-15 platform.

The next part I want to talk about on the AR-15 upper (it could have gone with the barrels but we'll keep with the upper components) is the gas tube and gas block. Your rifle relies on gas pressure to operate in the way that it was designed to. After you fire the AR-15, gas pressure forces the bolt carrier group into your buffer tube and a process that facilitates the ejection of a used round and the chambering of a new one.

Aero Precision Melonite Gas Tube

STNGR USA Low Profile Set Screw Gas Block .750" - AR15/M4

After you fire your rifle, gas moves behind the bullet that's leaving the barrel and moves through the gas port. Then it goes inside the gas block and it goes down the gas tube and exits through the bolt carrier's gas key. For the most part, the gas blocks are installed on the upper barrel inside the hand guard. The gas tube connects to the block on the upper receiver. And that's the gas tube and gas block of the AR-15.

The last part of the AR-15 rifle that I want to talk to you about is the part that helps keep the upper of your AR-15 clean. It's the ejection port cover. Now when this ejection port cover is closed it will prevent dirt, dust, and other debris from getting into the AR-15 and making it dirty. You want to keep your AR-15 upper as clean as possible, so that way it runs as flawlessly as possible.

Aero Precision AR15 Dust Cover Assembly. Image from Wing Tactical.