The AR platform has become a cornerstone of modern sporting rifles, known for its modularity, customization, and reliability. This versatility stems from the vast ecosystem of AR parts available on the market, allowing builders to create a rifle perfectly suited to their needs. Whether you’re a seasoned gunsmith or a first-time builder, understanding the components that make up an AR is crucial.
The Foundation: Upper and Lower Receivers At the heart of any AR-15 are the upper and lower receivers. These are the two main components that house all the other parts.
* Lower Receiver: This is the serialized part of the rifle, meaning it’s the component legally considered the “firearm.” It contains the trigger group, safety selector, magazine release, and the buffer tube. The lower receiver is the starting point for any build and must be purchased through a licensed dealer.
* Upper Receiver: The upper receiver houses the barrel, bolt carrier group (BCG), and charging handle. It’s the component responsible for cycling the ammunition. Upper receivers come in various styles, including flattop (with a picatinny rail) and fixed carry handle models. The Engine: The Barrel and Bolt Carrier Group The barrel and BCG are arguably the most critical parts for a rifle’s performance.
* Barrel: The barrel determines the rifle’s caliber, length, and accuracy potential. Barrels are available in a wide range of lengths (from pistol-length to rifle-length), profiles (lightweight, government, heavy), and materials (chrome-moly vanadium, stainless steel). The barrel’s twist rate is also a key factor, as it dictates how fast the bullet spins and can affect accuracy with different bullet weights.
* Bolt Carrier Group (BCG): The BCG is the “engine” of the rifle. It’s responsible for chambering the next round, firing, and ejecting the spent casing. A quality BCG is essential for reliable function. They are typically made of steel and often feature a protective coating like nitride or chrome to reduce friction and simplify cleaning. The Controls: Trigger, Handguard, and Stock These parts directly affect the shooter’s interaction with the rifle.
* Trigger: The trigger is the interface between the shooter and the firearm. Standard triggers are often serviceable, but many builders opt for an aftermarket trigger for a lighter pull, cleaner break, and shorter reset. Options range from single-stage to two-stage triggers, each offering a different feel.
* Handguard: The handguard protects the shooter’s hand from the hot barrel and provides a mounting platform for accessories like lights, lasers, and grips. Handguards come in various lengths and attachment systems, with M-LOK and KeyMod being the most popular choices today.
* Stock: The stock, or buttstock, provides a stable point of contact for the shooter. Stocks are available in fixed or adjustable configurations. Adjustable stocks are the most common, allowing the shooter to change the length of pull to fit their body and shooting style. Other Essential Parts Beyond the main components, a complete AR build requires several other parts:
* Charging Handle: Used to cycle the action and chamber the first round. Ambidextrous and extended charging handles are popular upgrades.
* Buffer and Buffer Spring: These are located in the buffer tube and help to absorb the recoil of the rifle’s action. The correct buffer weight and spring tension are critical for reliable cycling.
* Gas Block and Gas Tube: These components direct gas from the barrel to the BCG to cycle the action. The length of the gas system (carbine, mid-length, rifle) must match the barrel’s gas port location.
* Muzzle Device: This attaches to the end of the barrel and can serve various functions, such as a flash hider, compensator, or muzzle brake. Building Your Own AR The modularity of the AR platform means you can mix and match parts from different manufacturers to create a unique rifle. However, it’s essential to ensure all parts are compatible and properly installed. If you’re new to building, it’s always a good idea to start with a complete upper receiver or a builder’s kit to simplify the process.
Final Thoughts The world of AR parts is vast and ever-evolving. This guide provides a basic overview of the key components, but a deep dive into each part could fill a book. Whether you’re building a lightweight competition rifle, a rugged duty carbine, or a precision long-range shooter, the ability to select and assemble the perfect combination of parts is what makes the AR platform so enduringly popular. Happy building!