The AR-15 itself is made up of a few systems that all come together in the end to deliver an accurate shot that can cycle quickly and efficiently. The buffer assembly is responsible for mitigating recoil as well as providing the spring force necessary for the bolt to recycle ammunition from the magazine. The gas system is responsible for sending gas from the fired cartridge from the barrel back to the gas key on top of the bolt so that the recycling process can happen which entails the ejection of the spent cartridge and the addition of a new one. The trigger obviously is responsible for firing the ammunition.

Almost all of these require one important part in order to function, and that is the upper receiver. The upper receiver does a majority of the work when it comes to firing and cycling the action over the lower receiver. The lower receiver is really only meant to house the trigger group and the magwell and that’s about it. But why is the upper receiver such a heavy lifter? Why is there even an upper receiver in the first place? In this article we will go over the intricacies of the upper receiver, and what you can do to help your upper perform much better.

The upper receiver is quite possibly the most important part of the AR-15 as a whole. That is because, where the lower is meant really just to fire the ammunition, the upper receiver houses many of the components that directly affect the performance of the AR-15. That is especially since it contains the barrel, the gas system and the bolt, 3 of the main things that can severely affect your ARs performance whether good or bad.

What is the barrel of an AR-15?

The barrel of an AR-15 is actually made in two parts, and is one of the more stressful parts of the AR-15 to produce in high quantities. That is because manufacturers must be sure that the level of pressure the barrels are able to take meets the quality standard. Anything less could end a shooter up in the hospital or worse. The chamber is what connects to the AR-15 upper receiver, where the headspace must be near perfect in order to ensure a safe shot.

The AR-15 Gas System

The gas system of the AR-15 is a little more complex than the other parts and that is because of the sheer amount of calibers the AR-15 is able to take. Contrary to popular belief, it is actually a myth that an AR-15 gas system is a “one-size-fits-all.” The standard AR-15 gas system is really meant for either .223/ 5.56 NATO, although even then the pressure on a 5.56 NATO is a little higher than what you would want on your gas system.

The type of gas system you are using on your AR-15 build is important because it can directly affect the longevity of the other systems in the AR. That being the bolt and gas system itself, as well as the health of the bore over time. The buffer assembly can also suffer greatly. When there is too much gas entering the system, it is called overgassed. A good way to witness this happening is by looking at the round as it is ejecting. If the ejected cartridge is thrown out and behind you then that means the cartridge is overgassed. If the ejected cartridge is thrown out and in front of you, that means the system is undergassed. In this case, the buffer spring is able to start closing before the cartridge is able to fully eject, which springs the casing forward. A perfectly balanced system will eject the casing outward, perpendicularly to the orientation of the AR-15. However, this is something many AR-15 owners like to manipulate as you don’t need to swap out gas tubes, keys, or blocks in order to get this done. In this case, the parts of the buffer; the buffer spring and buffer weights can be changed to produce a different effect. When manipulating the gas system, you directly affect the longevity of the build, but that’s a given with most every modification you can make that isn’t simply adding furniture. The performance of your AR-15 for you is the most important part of owning your own AR-15.

Why switch out bolts?

Bolt carrier groups come in all shapes and sizes. The AR-15 bolt is a special one as it comes in a variety of different finishes. There are nickel-boron, phosphate, and nitride. Nickel boron and chrome lined bolts are the best of the bunch, but come at a much higher price. This is because they smoothen up the action, have anti-carbon build up properties even without using oil (always use gun oil) and generally have  a much nicer aesthetic appeal. Because of its anti carbon build up properties, maintenance  is much easier. Do NOT take that for an excuse to not clean your AR-15.

Nitride and phosphate barrels do not provide as much resistance to carbon build up, but can still offer a good amount of longevity if the gas key is chrome lined. This helps reduce wear and tear on the gas system as a whole, and helps fight against carbon build up in the gas key.

Bolts can still provide some aesthetic value to your AR-15 build as many companies offer different finishes to their bolts. Check those out here.

Conclusion The AR-15 upper receiver houses many of the AR-15’s core components. This means that you can modify the different parts of the upper to yield either an enhanced performance or a choppy one. Either way, knowing the functions of the AR-15 upper is key in modifying your AR-15 in the way you want it to perform.

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