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Demystifying the Modern AR15 Rifle: A Comprehensive Look at its Essential Components and Their Functionality

The AR15 rifle has earned a well-deserved reputation as a versatile and reliable firearm. At the heart of its success lies a precise assembly of various components that work in harmony to deliver exceptional performance. In this article, we’ll delve into the key parts that come together to create a modern AR15 rifle and explore how each component contributes to its overall functionality.

Upper Receiver:

The upper receiver is where the action happens. It houses critical parts such as the barrel, bolt carrier group (BCG), and charging handle. The upper receiver assembly is responsible for chambering rounds, extracting spent casings, and cycling the next round into the chamber.


The barrel plays a vital role in determining accuracy and range. Made from high-quality materials, such as chrome-moly steel or stainless steel, it provides stability and durability. The barrel’s twist rate affects bullet stabilization and accuracy, while its length influences muzzle velocity and maneuverability. For these reasons, the barrel is often considered the “heart” of the firearm. There are a ton of manufacturers out there that produce an equally wide variety of quality barrels as well. A good “in the middle” option is Ballistic Advantage or our line of JTF barrels.

Bolt Carrier Group (BCG):

microbest nitride bcg

The BCG is the heart of the AR15 rifle. It consists of the bolt, bolt carrier, and firing pin. As the rifle is fired, the BCG moves rearward, extracting and ejecting the spent casing, then chambers the next round from the magazine. It ensures reliable cycling and smooth functioning.


Lower Receiver:

The lower receiver serves as the foundation of the AR15 rifle. It houses the trigger mechanism, magazine well, and stock. Made from aluminum or polymer, it provides structural integrity and accommodates other essential components.

Trigger Group:

The trigger group determines the rifle’s firing capabilities and user experience. It comprises the trigger, hammer, disconnector, and springs. A quality trigger enhances accuracy, while proper sear engagement ensures safe operation. One of the largest manufacturers of reasonably priced, yet high quality triggers is Schmid Engineering and Tool.


Stock :

The stock provides stability and allows the shooter to properly shoulder the rifle. It may be fixed, collapsible, or adjustable to accommodate individual preferences and shooting scenarios. Comfort and ergonomics play a crucial role in stock selection. From fixed to adjustable and even specially designed precision stocks, there is a huge selection to choose from these days. A solid, dependable choice used by the military for years is the SOPMOD style of stock which features great ergonomics and even water resistant storage compartments.


The handguard protects the shooter’s hand from the heat generated by the barrel. It also provides a mounting platform for accessories like sights, lights, and grips. Various materials, such as polymer, aluminum, or carbon fiber, offer different levels of durability and weight savings. Popular options include mounting options such as the M-LOK system developed by Magpul or the 1913 Picatinny rail system which was in part developed by the US Army.


Gas System:

The gas system regulates the flow of propellant gases to operate the rifle. Most AR15 rifles employ a direct impingement or gas piston system. The gas block, gas tube, and gas key work together to control gas flow, ensuring reliable cycling and reduced recoil. Common gas tube sizes seen on the platform include pistol, carbine, mid length, and rifle and vary in length with pistol being the shortest and rifle being the longest. A wide variety of gas blocks also exist and often include “fixed” and “adjustable” types. Adjustable gas blocks allow the operator to increase or reduce the flow of gas returning to the upper to cycle the action. This can be a benefit for those shooting suppressed, which often forces more gas into the gun due to increased back pressure. Drawback also exist, such as an increase in the number of parts, therefore increasing the points of failure on a firearm.


The magazine is responsible for storing and feeding ammunition into the rifle. AR15 rifles commonly use detachable box magazines with various capacities. Quality magazines ensure reliable feeding, reducing malfunctions during operation.

Buffer System:

The buffer system comprises of the receiver extension (also called buffer tube by some), recoil or buffer spring, buffer weight and typically a castle nut and end plate to attach and secure the assembly to the lower receiver. This assembly of parts plays a massively important roll in the function and reliability of the AR 15 platform. The AR, like many mechanical devices, is a balance between forces in action. Pressure, velocity and friction just to name a few. If anything is out of balance, the system begins to malfunction. For example, if your BCG is moving to fast while cycling, it may fail to properly extract a spent cartridge or feed a fresh one.

Here at JTF we generally recommend the following setups for carbine buffer systems:

  • 14.5 to 16 inch 5.56 carbine gas system = Minimum Sprinco White, Red White, or Red spring and H1 Buffer
  • 14.5 to 16 inch 5.56 mid length gas system = Sprinco Blue spring and H1 Buffer
  • Less than 14.5 inch carbine or pistol gas systems = Red/White, Red or Blue Spring with an H1 or H2 buffer

These setups will change based on your barrel’s gas port size and if you add a suppressor into the mix or not, so don’t be afraid to consult one of our armorers if you have questions for your specific setup.


The modern AR15 rifle is an engineering marvel, comprising several intricately designed components that work synergistically to deliver accuracy, reliability, and versatility. From the upper receiver to the magazine, each part plays a vital role in the rifle’s overall functionality. Understanding these components and their interactions is key to appreciating the craftsmanship behind this iconic firearm.

Whether you’re a seasoned shooter or an aspiring enthusiast, gaining insight into the inner workings of the AR15 rifle enhances your appreciation for its precision engineering. As you assemble or upgrade your own AR15, remember that the quality and compatibility of each component contribute to the rifle’s performance and your shooting experience.

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