Building an AR15 - A Builder's Parts List

Introduction

The AR15 rifle is known for its versatility, and stands out as a favorite among gun enthusiasts and builders. Its modular design allows for a wide range of modifications, enabling users to tailor their rifles to specific preferences or operational needs. Understanding each component of the AR15 is crucial for anyone looking to begin a custom build. This knowledge not only enhances the building experience but also ensures the creation of a reliable firearm. Whether for sport, hunting, or defense, the journey to building your AR15 starts with a deep dive into its essential parts and their functions.

In the next sections, we'll explore the key components of a modern AR15 rifle to better equip you with the knowledge you need to put together a successful and highly satisfying build.

The AR15 Component Considerations

Before getting into the specifics of what makes up an AR15 build, let's discuss some essential and foundational considerations all AR15 builders should think about before starting their build.

1. Compatibility: Take some extra time to ensure that all components are compatible with each other and adhere to mil-spec dimensions. This helps to avoid issues of poor fitment or complete malfunction.  Be aware, many manufacturers advertise the specific part they manufacture is better than mil-spec, but too many non-mil-spec variations of parts in a build can lead to major compatibility issues.  If you decide to go the route of a non-mil-spec or "better than mil-spec" build, try to stick with the same manufacturer for all your components, it will save you from a headache that may develop half-way into your build.
2. Quality: Invest in high-quality components from reputable manufacturers to ensure reliability, durability, and optimal performance.  In our experience, the cost/quality chart tends to look more like an exponential trend where you start off getting much higher quality by spending a bit more, but that tapers off and becomes almost all cost and little benefit after you hit a certain point.  Your mid-tier rifles are the best bang for the buck in our opinion, but we'll let you argue with your buddies about what companies manufacture low, mid, and upper tier parts and rifles.  Quality control is the name of the game when most companies are manufacturing the exact same parts.
3. Tools: Be sure to acquire the necessary tools and equipment for assembly, including a vise, vise blocks, torque wrenches, and pin punches, to prevent damage to components and ensure proper assembly. We offer quite a few tools and kits to get you started.
4. Functionality: Consider your intended use for the firearm and select components that align with your needs and preferences. Whether it be precision shooting, tactical applications, or competition, the aftermarket for AR15 parts is expansive and has specific parts for most any niche you're looking to build for.  Just like if you were building a car to race, you wouldn't build an off road rally car the same way you'd build a formula one race car.
5. Legal Considerations: Familiarize yourself with local laws and regulations regarding the assembly and ownership of firearms to ensure compliance and avoid legal repercussions.  While all gun laws are unconstitutional, that argument won't prevent you from getting thrown in federal prison (or get your family murdered like Randall Weaver...look up "Ruby Ridge") for ignoring those laws on the books.  If you live in a state that has been overtaken by commies and idiots, keep fighting the good fight and think about donating to the guys who are battling it out in the courts on your behalf like FPC (Firearms Policy Coalition) or joining as a member (we get no compensation for donations or membership).  The NRA will still fight some battles on your behalf, but sadly, they caved long ago on being 2nd amendment absolutists.

With that established, building an AR15 rifle from scratch or upgrading an existing one requires a solid understanding of its fundamental parts. Each component plays a specific role in the rifle's operation, affecting its performance, looks, and ergonomics. OKAY, now let's finally delve into the parts that make up a modern AR15 build.

Lower Receiver

The lower receiver is considered the heart of the AR15, housing the fire control group (trigger, hammer, and safety), magazine well, and attachment points for the buffer kit/stock and upper receiver. As the only standard part of the rifle that's federally regulated, it bears the serial number and is technically considered the firearm itself. This is the one part you won't be able to ship direct to your home and will have to ship to a local FFL to conduct the transfer.  

Selecting a lower receiver involves choices between materials (aluminum, polymer, or specialty alloy), construction (forged, billet, cast, or printed) and whether you want to start with just the bare lower receiver (stripped) or the lower receiver with all the parts installed (complete).  You can also buy an 80% lower and do the millwork yourself, but we'd suggest at least acquiring a stripped lower receiver that's already been machined to the right specs to prevent any unnecessary headaches from the start, but to each their own.

If you decide to purchase a stripped lower and assemble it yourself, thank God you don't have to buy all the lower parts separately. Everything can be purchased in a lower parts kit that includes all the small required parts to complete a stripped lower.

Here are all the lower receiver parts and their function:

• Lower Receiver (Stripped): The main component that houses the the fire control group (trigger, hammer, and safety), magazine well, and attachment points for the buffer kit/stock and upper receiver.  Marked with the manufacturer, model, caliber, and serial number, this one part must be shipped to a local FFL to have a background check and paperwork completed since it's the one regulated part that's considered the gun by the federal government.  Be sure to check state and local laws for any additional requirements for acquiring a lower receiver.
• Buffer Retainer: The buffer retainer is a small metal piece that retains the buffer and recoil spring within the lower receiver. It ensures proper functioning of the firearm by holding these components in place during operation (included in most lower parts kits).
• Buffer Retainer Spring: This spring applies tension to the buffer retainer, keeping it engaged and maintaining its position within the lower receiver (included in most lower parts kits).
• Takedown Pin Spring: The takedown pin spring applies pressure to the takedown pin, ensuring it stays in place while still allowing for easy disassembly of the firearm (included in most lower parts kits).
• Takedown Pin Detent: This small metal piece interacts with the takedown pin, holding it securely in either the open or closed position (included in most lower parts kits).
• Takedown Pin: Takedown pins hold the upper and lower receiver together and allow for the separation of the upper and lower receivers for maintenance and cleaning. They allow for quick and tool-less disassembly of the firearm (included in most lower parts kits).
• Safety Detent: The safety detent is a small component that interacts with the safety selector, providing tactile feedback when switching between safe and fire modes (included in most lower parts kits).
• Safety Detent Spring: This spring applies pressure to the safety detent, ensuring it engages properly with the safety selector (included in most lower parts kits).
• Safety Selector: The safety selector is a lever located on the side of the lower receiver that allows the shooter to engage or disengage the firearm's safety mechanism (included in most lower parts kits)..
• Pistol Grip Screw (with Lock Washer): The pistol grip screw, along with the lock washer, secures the pistol grip to the lower receiver (included in most lower parts kits).
• Pistol Grip: The pistol grip is the handle portion of the firearm where the shooter's hand grips the weapon. It provides control and stability during firing. There are tons of grip options to purchase, so we would suggest getting your hands on different options to determine what feels the best. This is the one spot your hand will be engaged 100% of the time while using your your rifle, so you want it to feel right for your grip.
• Bolt Catch: The bolt catch is a device that holds the bolt carrier group open after the last round is fired, facilitating easier reloading of the firearm (included in most lower parts kits).
• Bolt Catch Roll Pin: This pin secures the bolt catch in place within the lower receiver (included in most lower parts kits).
• Bolt Catch Plunger: The bolt catch plunger is part of the mechanism that engages the bolt catch, allowing it to function properly (included in most lower parts kits).
• Bolt Catch Spring: This spring provides tension to the bolt catch mechanism, ensuring it operates smoothly.
• Magazine Catch: The magazine catch is a button or lever located on the side of the lower receiver that releases the magazine for removal (included in most lower parts kits).
• Magazine Catch Button: The magazine catch button is the part of the magazine catch mechanism that the shooter presses to release the magazine (included in most lower parts kits).
• Magazine Catch Spring: This spring applies pressure to the magazine catch, ensuring it engages properly with the magazine (included in most lower parts kits).
• Pivot Spring Pin: This pin secures the pivot pin in place within the lower receiver (included in most lower parts kits).
• Pivot Pin Detent: Similar to the takedown pin detent, this small metal piece interacts with the pivot pin, holding it securely in place (included in most lower parts kits).
• Pivot Pin: The pivot pin is another component used to separate the upper and lower receivers of the AR-15. It works in conjunction with the takedown pin for disassembly (included in most lower parts kits).
• Trigger Guard Pivot Roll Pin: This pin secures the trigger guard assembly to the lower receiver, allowing it to pivot for trigger access (included in most lower parts kits).
• Trigger Guard Assembly: The trigger guard assembly encompasses the trigger guard and sometimes includes the roll pin and spring for attachment (included in most lower parts kits).
• Trigger: The trigger is a critical component of the firing mechanism, initiating the firing sequence when pulled. While this is standard in most lower parts kits, there are MANY OPTIONS for aftermarket triggers that will enhance your shooting experience with different pull weights and crisp breaks.
• Disconnector Spring: This spring provides tension to the disconnector, allowing it to reset after each firing cycle (included in most lower parts kits).
• Disconnector: The disconnector is part of the trigger mechanism that ensures the firearm fires in a semi-automatic mode, preventing full-auto fire (included in most lower parts kits).
• Trigger Spring: The trigger spring provides tension to the trigger, allowing for a crisp and consistent trigger pull (included in most lower parts kits).
• Hammer and Trigger Pins: These pins secure the hammer and trigger assemblies within the lower receiver, allowing them to pivot and function properly (included in most lower parts kits).
• Hammer Spring: The hammer spring provides the necessary force to reset the hammer after each firing cycle, preparing it for the next shot (included in most lower parts kits).
• Hammer with J Pin: The hammer is a critical component of the firearm's firing mechanism. It strikes the firing pin to ignite the primer of a cartridge, firing the round. The J pin is part of the hammer assembly, aiding in its function (included in most lower parts kits).
• Magazine: The magazine is the removable container that holds cartridges and feeds them into the firearm's chamber for firing. High quality magazines are essential for feeding ammunition reliably during operation.  You'll want to acquire a handful of magazines, so you don't have to stop and reload your magazine each time you run out of ammo. *Shooters Tip: If you're having issues with your rifle cycling consistanly, the first step in troubleshooting that issue is always grab a different magazine first to ensure it's not the culpret.  It's not uncommon to have a damaged or out of spec magazine contributing to your rifle not cycling, plus it's a cheap and easy fix!

NOTE: The buffer kit and stock are typically considered part of the lower but we'll be covering those essential components separately later.

Upper Receiver

The upper receiver contains the charging handle, bolt carrier group, gas system, barrel, and handguard. It's where the action happens after a round is fired and is also where most of your build money should be spent. The upper can be customized for various purposes, including different barrel lengths and calibers, handguard types, and optics mounting solutions. Compatibility with the lower receiver is crucial for a seamless fit and operation.  Most compatible upper receivers can be quickly swapped to different lowers and allow you to change your rifle setup without having to buy a separate complete lower.

Here are all the upper receiver parts and their function:

• Upper Receiver Housing (Stripped): The upper receiver housing is the portion of the AR-15 that contains the charging handle, bolt carrier group, and mates with the barrel, barrel nut, and handguard.  This is one of teh fundamental components that play a major role in the accuracy of your rifle.
• Charging Handle: The charging handle is used to manually chamber a round in the AR15 by pulling it backward then letting it go. The latch is the mechanism that locks it into place, and the spring returns it to its forward position after use. The roll pin secures various parts of the charging handle assembly.
• Forward Assist (Spring Pin, Plunger, prawl spring pin, prawl spring, pawl detent, prawl): The forward assist is a feature designed to help push the bolt into battery if it fails to fully close. It typically consists of several components, including the spring pin, plunger, prawl spring pin, prawl spring, pawl detent, and prawl. While there are numerous upper receivers manufactured without a forward assist, most opt for an upper with one...just in case.
• Ejection Port Cover (cover, cover pin, ring, cover spring): The ejection port cover is a hinged cover that protects the ejection port from debris and fouling. It typically consists of the cover pin, ring, and cover spring, which work together to allow the cover to open and close as needed.
• Handguard: The handguard is a protective covering that surrounds the barrel of the AR-15. It provides a gripping surface for the shooter and can also serve as a mounting point for accessories such as lights, lasers, front sights, and grips.  Almost every company has their own handguard, so if you don't like the way one looks, there's 1000 other options to choose from.
• Barrel Nut: The barrel nut secures the barrel to the upper receiver and provides a mounting point for the handguard. One typically comes with the purchase of a handguard and must be tightened to a specific torque to ensure proper alignment and stability. Normally, you can expect one to come with the handguard that will affix the barrel and handguard to the upper receiver.
• Gas Block (clamp or screw): The gas block regulates the flow of gas from the barrel to the gas tube, which cycles the action of the rifle. It can be attached to the barrel using a clamp or screws, depending on the design.  Some even opt to have their gas block pinned to the barrel to ensure it never comes loose.
• Gas Tube (tube and roll pin): The gas tube transfers gas from the barrel to the bolt carrier group, cycling the action of the rifle. It is typically secured to the gas block and upper receiver using a roll pin. This method of triggering the action of the rifle is referred to as "direct impingement."
• *Barrel: The barrel is the long, cylindrical metal tube through which the bullet travels when the firearm is fired. It is rifled to impart spin on the projectile for stability and accuracy. *Additional information about barrels discussed later.
• Crush Washer: The crush washer is a specially designed washer used to properly align and secure muzzle devices such as flash hiders, compensators, or muzzle brakes. It helps ensure that the muzzle device is oriented correctly and prevents gas leakage.
• Muzzle Device: The muzzle device is attached to the end of the barrel and serves various purposes, including reducing recoil, redirecting muzzle blast, and reducing flash. Examples include flash hiders, compensators, and muzzle brakes.
• *Carry Handle with Rear Sight: The carry handle serves as a mounting point and carrying device for the AR-15 rifle. Additionally, it often integrates a rear sight, allowing for aiming and target acquisition. * This is an optional part and is not required for those looking to install an optic or flip-up sights. 

Barrel

In the realm of AR-15 customization, few components are as critical to performance as the barrel. It's the conduit through which bullets travel, affecting accuracy, range, and overall shooting experience. But with a plethora of options available, navigating the world of AR-15 barrels can be daunting. Fear not, as we embark on a journey to explore the nuances of AR-15 barrels, the myriad options available, and the essential considerations for builders.

An AR-15 barrel isn't just a metal tube...well...technically it is BUT...it's really a carefully crafted piece of engineering that can significantly impact your accuracy and shooting experience. Here are some key aspects to consider:

• Length: Barrels come in various lengths, ranging from compact 10.5-inch models to rifle-length 20-inch barrels. Longer barrels generally offer better accuracy and velocity due to increased dwell time and sight radius, while shorter barrels are more maneuverable in tight spaces.
• Profile: The profile refers to the shape and thickness of the barrel. Common profiles include government, lightweight, medium, and heavy. Each profile offers a balance of weight, heat dissipation, and rigidity, catering to different shooting styles and preferences.
• Material: AR-15 barrels are typically made from stainless steel or chrome-moly steel. Stainless steel barrels offer superior corrosion resistance and are often preferred for precision shooting, while chrome-moly barrels are more affordable and offer excellent durability.
• Twist Rate: The twist rate refers to the rate of rifling twist within the barrel, expressed as one full rotation over a certain distance (e.g., 1:7 means one complete rotation every seven inches). The twist rate affects the stability and accuracy of different bullet weights, with faster twist rates generally better suited for heavier projectiles.
• Chamber: The chamber is the portion of the barrel where the cartridge is seated before firing. Common chamber options include .223 Wylde, 5.56x45mm NATO, and .300 Blackout, each designed for specific cartridges and applications.

Now that we've covered the basics, let's delve into some popular AR-15 barrel types and profiles:

• Match Grade Barrels: These barrels are precision-machined to tighter tolerances and often feature hand-lapped bores for enhanced accuracy. Match grade barrels are favored by competitive shooters and precision rifle enthusiasts seeking maximum performance.
• Pencil Barrels: Characterized by their slim profile and lightweight construction, pencil barrels are ideal for shooters prioritizing weight reduction and maneuverability. They excel in applications where rapid target transitions and handling are paramount.
• Fluted Barrels: Fluting involves machining grooves or channels along the length of the barrel to reduce weight and improve heat dissipation. Fluted barrels offer a balance of rigidity and weight savings, making them popular among competition shooters and hunters.
• Chrome-Lined Barrels: Chrome-lined barrels feature a layer of chrome plating inside the bore, offering increased resistance to corrosion and erosion. They are highly durable and well-suited for high-volume shooting and adverse environmental conditions.
• Carbon Fiber Barrels: Carbon fiber barrels are crafted using advanced composite materials that consist of carbon fibers embedded in a polymer matrix. This construction results in a barrel that is significantly lighter than traditional steel barrels while maintaining exceptional strength and rigidity.

Here's some essential considerations builders should take into account when deciding on a rifle barrel:

• Purpose: Determine the intended use of your AR-15 build, whether it's long-range precision shooting, tactical applications, or home defense. Select a barrel that aligns with your shooting goals and preferences.
• Budget: Set a realistic budget for your build and prioritize components accordingly. While premium barrels offer superior performance, there are plenty of budget-friendly options available that deliver excellent value.
• Compatibility: Ensure compatibility between the barrel, chamber, gas system, and other components of your AR-15 build to prevent issues such as reliability issues or malfunctions.
• Research: Take the time to research and read reviews from reputable sources to gain insights into the performance and reliability of different barrel options. Consider factors such as accuracy, durability, and manufacturer reputation when making your decision.
• Quality Control: Invest in barrels from reputable manufacturers known for their quality control processes and attention to detail. Quality barrels undergo rigorous testing and inspection to ensure consistent performance and reliability.

Bolt Carrier Group (BCG)

In the intricate world of AR-15 customization, few components play a more crucial role than the bolt carrier group (BCG). Serving as the heart of the rifle's action, the BCG is responsible for chambering, firing, extracting, and ejecting rounds with precision and reliability. As builders seek to optimize their AR-15 builds, understanding the nuances of BCGs and the various options available becomes paramount. In this article, we'll delve into the intricacies of AR-15 bolt carrier groups, explore the different options, and highlight essential considerations for builders.

Anatomy of an AR-15 Bolt Carrier Group:

Before we explore the different options available, let's dissect the components that comprise an AR-15 bolt carrier group:

1. Bolt: The bolt is the primary component responsible for locking into the barrel extension, extracting spent casings, and chambering new rounds. It consists of a bolt head, extractor, ejector, and gas rings, all of which work in tandem to ensure reliable operation.
2. Carrier: The carrier houses the bolt and reciprocates within the upper receiver during the firing cycle. It features a gas key that interfaces with the gas tube, transferring gas pressure to cycle the action. The carrier also includes a cam pin that interfaces with the bolt, allowing it to rotate and lock into the barrel extension.
3. Gas Key: The gas key is securely staked to the carrier and interfaces with the gas tube. It channels hot gases from the barrel into the carrier, initiating the cycling process. Proper staking of the gas key is essential to prevent gas leakage and ensure reliable operation.
4. Firing Pin: The firing pin protrudes from the bolt and strikes the primer of the cartridge, initiating ignition. It is retained within the bolt carrier group by a firing pin retaining pin.
5. Cam Pin: The cam pin facilitates the rotational movement of the bolt within the carrier. It fits into a cam slot machined into the bolt and reciprocates with the carrier during the firing cycle.

Exploring BCG Options:

Now that we understand the components of an AR-15 bolt carrier group, let's explore the different options available to builders:

1. Standard AR15 BCG: Designed for semi-auto rifles only, the standard AR15 BCG features a full mass carrier and is the most commonly used configuration. It strikes a balance between durability, reliability, and cost-effectiveness, making it suitable for a wide range of applications.
2. Standard (Full-Auto) M16 BCG: Designed for full-auto/select-fire rifles only, the standard M16 BCG features a full mass carrier and is the most commonly used configuration. It strikes a balance between durability, reliability, and cost-effectiveness, making it suitable for a wide range of applications.
3. Low-Mass / Lightweight BCG: Lightweight BCGs feature material removal from non-essential areas to reduce overall weight. This weight reduction can improve cyclic rate and reduce felt recoil, making lightweight BCGs popular among competition shooters and those seeking faster follow-up shots.
4. Nickel Boron (NiB) Coated BCG: NiB coatings provide enhanced lubricity and corrosion resistance compared to traditional phosphate or chrome finishes. NiB-coated BCGs are easier to clean and maintain, making them ideal for shooters operating in harsh environments or those seeking minimal maintenance requirements.
5. Low-Mass BCG: Low-mass BCGs feature further material reduction for even greater weight savings. These BCGs are often paired with lightweight barrels and other components to create ultra-lightweight AR-15 builds optimized for speed and maneuverability.
6. Adjustable Gas Key: Some BCGs feature an adjustable gas key that allows users to fine-tune gas pressure for optimal performance. This feature is particularly useful for shooters using suppressors or those seeking to optimize their AR-15's cycling characteristics.

BCG Coatings and Finishes:

There are quite a few different coatings and finishes available for bolt carrier groups (BCGs), each with its own set of advantages and disadvantages. Here's a list of some common BCG coatings and their pros and cons:

1. Phosphate (Parkerized):
   • Pros:
     • Corrosion Resistance: Phosphate coatings provide a good level of protection against rust and corrosion.
     • Durability: Phosphate finishes are relatively durable and offer good wear resistance.
     • Cost-effective: Phosphate coatings are typically more affordable compared to some other coatings.
   • Cons:
     • Friction: Phosphate finishes may have higher friction compared to some other coatings, potentially affecting smoothness of operation.
     • Maintenance Requirements: While phosphate coatings provide good corrosion resistance, they may require more frequent cleaning and lubrication compared to some other premium finishes. Proper maintenance is essential to ensure long-term protection and performance.
2. Black Nitride (Salt Bath Nitride or Melonite):
   • Pros:
     • Corrosion Resistance: Black Nitride coatings provide excellent resistance to corrosion and rust. The process creates a hard, durable surface layer that protects the underlying metal from moisture, salt, and other environmental factors.
     • Wear Resistance: Black Nitride coatings offer high wear resistance, making them ideal for high-friction firearm components like BCGs. This results in extended service life and reduced maintenance requirements.
     • Improved Lubricity: The surface finish of Black Nitride-coated BCGs is inherently lubricious, meaning it reduces friction between moving parts. This results in smoother operation, reduced fouling, and easier cleaning.
     • Enhanced Hardness: Black Nitride treatments increase the surface hardness of the BCG, improving its resistance to scratching, abrasion, and deformation. This helps maintain dimensional stability and reliability under harsh conditions.
     • Aesthetics: Black Nitride coatings create a sleek, matte-black finish that is highly desirable among firearm enthusiasts. The uniform appearance adds a professional touch to the firearm's overall aesthetic.
     • Cost-Effectiveness: Compared to some other premium coatings like Nickel Boron or Titanium Nitride, Black Nitride is often more cost-effective while still offering excellent performance and durability.
   • Cons:
     • Color Variability: While Black Nitride typically produces a deep black finish, slight variations in color may occur depending on the specific process and application. Some users may prefer a more consistent appearance.
     • Limited Availability: While Black Nitride-coated BCGs are becoming increasingly popular, they may not be as widely available as more traditional finishes like phosphate or chrome, but many reputable manufacturers offer Black Nitride options.
3. Nickel Boron (NiB):
   • Pros:
     • Corrosion resistance: Nickel Boron coatings offer excellent resistance to corrosion and oxidation. The coating forms a protective barrier that prevents moisture and contaminants from reaching the underlying metal, reducing the risk of rust and corrosion.
     • Low friction: Nickel Boron coatings have inherently low friction properties, resulting in smoother operation of the BCG. This reduces the likelihood of fouling, carbon buildup, and malfunctions, particularly in adverse conditions.
     • Easy to clean: The slick surface of NiB-coated BCGs makes them easy to clean and maintain. Residue and fouling are less likely to adhere to the surface, allowing for quick and effortless cleaning with minimal lubrication required.
   • Cons:
     • Cost: NiB coatings are typically more expensive compared to phosphate or nitride finishes.
     • Color variation: Some NiB coatings may exhibit slight color variation, which can be a cosmetic concern for some users.
     • Exercise caution when purchasing a NiB BCG.  Some manufacturers have issues with the NiB coating flaking off with wear, so be sure to choose a reputible company who's utilizing the current NiB technology where the coating flaking with wear has basically become a non-issue.  UCT Coating's EXO NiB (FailZero's parent company) is the industry leader in nickel boron coatings and handles a large percentage of the NiB coatings on BCGs for major manufacturers in the USA.
4. Hard Chrome:
   • Pros:
     • Corrosion Resistance: Hard chrome plating provides excellent resistance to corrosion and oxidation. The thick chrome layer forms a protective barrier that shields the underlying metal from moisture, chemicals, and environmental contaminants.
     • Wear Resistance: Hard chrome coatings offer exceptional hardness and wear resistance. The durable surface layer is highly resistant to scratching, abrasion, and friction, resulting in extended service life and improved reliability.
     • Smooth Operation: Hard chrome coatings have low friction properties, resulting in smoother operation of the BCG. This reduces wear on moving parts, minimizes fouling and carbon buildup, and enhances overall performance.
     • Easy Cleaning: The slick surface of hard chrome-coated BCGs makes them easy to clean and maintain. Residue and fouling are less likely to adhere to the surface, allowing for quick and effortless cleaning with minimal lubrication required.
     • Heat Resistance: Hard chrome plating can withstand high temperatures without degradation or loss of protective properties. This makes it suitable for sustained firing sessions and high-volume shooting without sacrificing performance or reliability.
     • Aesthetics: Hard chrome plating produces a bright, reflective finish that is visually appealing and adds a premium look to the firearm. The uniform appearance of the chrome coating enhances the overall aesthetics of the BCG.
   • Cons:
     • Cost: Chrome finishes tend to be more expensive compared to phosphate or other coatings. Hard chrome plating requires specialized equipment and expertise for proper application. The process involves electroplating the BCG with multiple layers of chromium, which adds to the complexity and cost of production.
     • Limited Availability: While hard chrome-coated BCGs are available from some manufacturers, they may not be as readily available as more common finishes like phosphate, black nitride, or nickel boron. However, many reputable manufacturers offer hard chrome options for those seeking enhanced performance and durability.
5. Titanium Nitride (TiN):
   • Pros:
     • Hardness: Titanium Nitride coatings are extremely hard, offering exceptional wear resistance. The hard surface layer protects the underlying metal from scratching, abrasion, and friction, resulting in extended service life and improved reliability.
     • Corrosion resistance: TiN coatings provide excellent resistance to corrosion and oxidation. The thin layer of titanium nitride forms a protective barrier that prevents moisture, chemicals, and environmental contaminants from reaching the underlying metal.
     • Low Friction: Titanium Nitride coatings have inherently low friction properties, resulting in smoother operation of the BCG. This reduces wear on moving parts, minimizes fouling and carbon buildup, and enhances overall performance.
     • Heat Resistance: Titanium Nitride coatings can withstand high temperatures without degradation or loss of protective properties. This makes them suitable for sustained firing sessions and high-volume shooting without sacrificing performance or reliability.
     • Aesthetics: Titanium Nitride coatings produce a bright gold or copper-colored finish that is visually striking and adds a custom look to the firearm. The vibrant color and uniform appearance of the coating enhance the overall aesthetics of the BCG.
   • Cons:
     • Cost: TiN coatings are among the most expensive options due to the specialized coating process and premium materials.
     • Limited availability: TiN-coated BCGs may be less readily available compared to other finishes. However, many reputable manufacturers offer TiN options for those seeking enhanced performance and aesthetics.
6. Diamond-Like Carbon (DLC):
   • Pros:
     • Hardness: DLC coatings are extremely hard and offer exceptional wear resistance. The diamond-like structure provides superior protection against scratching, abrasion, and friction, resulting in extended service life and improved reliability.
     • Corrosion resistance: DLC coatings provide excellent resistance to corrosion and oxidation. The durable surface layer forms a protective barrier that prevents moisture, chemicals, and environmental contaminants from reaching the underlying metal. DLC coatings are chemically inert and resistant to a wide range of solvents, oils, and cleaning agents. This makes them easy to clean and maintain, with minimal risk of damage or degradation from harsh chemicals.
     • Low friction: DLC coatings have inherently low friction properties, resulting in smoother operation of the BCG. This reduces wear on moving parts, minimizes fouling and carbon buildup, and enhances overall performance.
   • Cons:
     • Cost: DLC coatings can be expensive due to the premium materials used in the advanced manufacturing process.
     • Limited availability: DLC-coated BCGs may be less common and more difficult to find compared to other finishes.
7. Cerakote:
   • Pros:
     • Customization: Cerakote finishes offer virtually unlimited color options, allowing for complete customization.
     • Corrosion resistance: Cerakote provides good resistance to corrosion, especially when properly applied.
     • Scratch resistance: Cerakote coatings are highly resistant to scratching and abrasion.
   • Cons:
     • Application complexity: Cerakote requires specialized equipment and expertise for proper application, which may increase cost.
     • Durability: Cerakote coatings are highly durable and resistant to wear, abrasion, and scratching. The tough ceramic-based finish helps protect the BCG from damage and maintains its appearance over time.
     • Limited thickness: Cerakote coatings are relatively thin, typically measuring only a few microns in thickness. While this helps maintain tolerances and fit within the firearm, it may not provide the same level of protection as thicker coatings or platings.
     • *Even though it's becoming more common, Aerospace Arms does not advise applying Cerakote to a high-tolerance item like a BCG.

At the core of the rifle's functionality, the BCG consists of the bolt, carrier, gas key, and firing pin. It plays a crucial role in the rifle's cycling process, affecting reliability and rate of fire. Quality and material choice in the BCG can significantly impact the AR15's performance under different conditions.

Gas System

The gas system is an essential part of  your gun operating, utilizing propellant gas from a fired round to cycle the action. The length of the gas system (pistol, carbine, mid-length, or rifle) affects the rifle's recoil and shooting experience. A properly tuned gas system ensures smooth operation and minimizes wear on the rifle's components.  The gas system is determined by the location of the port on the barrel along with the diameter of the barrel, so when you order your barrel, pay attention to the length of gas tube and size (diameter) of gas block you'll need.

Handguard

Handguards protect the shooter's hand from the hot barrel and provide mounting space for a front sight and accessories like forgrips lights, lasers, and other accessories. They come in free-floating or drop-in styles, with free-floating handguards offering improved accuracy by not contacting the barrel. Material and design choices can affect the rifle's weight and balance.  Be sure to pay attention to the mounting system of the handguard so you know what mounts your accessories need to have to attach to the handguard.

Stock and Buffer System

The stock and buffer system both play a unique role in the rifle's operation, comfort, and performance. Let's dive deeper into these components, understanding the parts and their functions within the system.

Stocks

The stock of an AR15 is the part that rests against the shooter's shoulder, providing support and stability when firing. It's an essential component for aim and comfort, affecting the rifle's overall ergonomics and handling. Stocks come in various forms, but primarily categorized into two types: fixed and adjustable.

• Fixed Stocks: These stocks have a solid, non-moving design. They are known for their stability and are often preferred for precision shooting or longer-range applications where a consistent cheek weld and stock placement are crucial. Fixed stocks can also provide additional storage space for batteries or small tools and can be more durable due to their lack of moving parts.
• Adjustable Stocks: Adjustable or collapsible stocks allow the shooter to change the length of pull (the distance from the trigger to the end of the stock) to fit different body sizes, armor, or shooting positions. This versatility makes them popular for tactical and general-purpose builds. They typically feature a series of notches or a friction lock system for adjustment.

Buffer System

The buffer system is housed inside the stock and plays a pivotal role in the rifle's cycling process. It consists of the buffer tube (or receiver extension), buffer spring, and buffer. This system helps manage recoil and ensures the smooth operation of the bolt carrier group (BCG) after each shot. Here's a breakdown of its components:

• Buffer Tube (Receiver Extension): This tube extends from the rear of the lower receiver and houses the buffer and buffer spring. It also serves as the attachment point for the stock. Buffer tubes come in two main sizes: commercial and mil-spec, which differ slightly in diameter.
• Buffer Spring: The buffer spring sits inside the buffer tube, pushing the buffer (and thus the BCG) forward into the ready position after the recoil from a shot has pushed it backward. The spring's tension and length can affect the rifle's cycling rate and perceived recoil.
• Buffer: The buffer itself is a weighted cylinder that moves within the buffer tube, absorbing the recoil and slowing down the BCG as it cycles. Buffers come in various weights, allowing shooters to fine-tune the rifle's performance based on the caliber, gas system length, and ammunition used. Heavier buffers can reduce felt recoil and smooth out the cycling process, but they may require adjustments to the gas system for optimal performance.
• End Plate: A flat metal plate that attaches to the rear of the lower receiver, securing the rear of the buffer tube in place. It typically features sling attachment points for attaching a sling to the rifle.
• Castle Nut: A notched, cylindrical nut that threads onto the buffer tube, securing it to the lower receiver. It is tightened against the end plate to prevent the buffer tube from rotating and loosening during use.

The stock and buffer system work together to provide stability, comfort, and reliability in the AR15 platform. Choosing the right stock and buffer kit involves considering the intended use of the rifle, the shooter's preferences for ergonomics and adjust-ability, and the specific requirements of the build's other components, like the barrel length and gas system. A well-selected stock and buffer system can significantly enhance the shooting experience, offering a balance of comfort, control, and performance.

Sights and Optics

We could (and probably should) write an entire article on alone on these components, so we'll keep it short and to the point.  Iron sights or back-up sights, whether fixed or flip-up, provide a more traditional and reliable aiming solution. For enhanced accuracy and range, optics like red dots, holographic sights, and scopes can be mounted to the upper receiver. Choosing the right sights or optics depends on the intended use, such as close-quarters combat (CQC) or long-range shooting.

Accessories and Customization

Beyond the core components, there is a plethora of accessories and custom parts you can buy to further personalize an AR15. Enhanced triggers for smoother operation, ergonomic grips for better control, ambidextrous options for most every part, or a chainsaw to mount up front in case you're out of ammo and the zombie horde won't stop coming...not sure why else you'd want one mounted on your AR, but they're available ( I'm not kidding).  Just know, there are thousands of customization options for your AR15 build and more coming out daily.

Conclusion

Understanding each component of the AR15 allows builders to tailor their rifles to their specific needs, whether for competitive shooting, hunting, or defense. The modular nature of the AR15 platform offers endless possibilities for customization, making every build unique. With the right knowledge and tools, building an AR15 can be an immensely satisfying journey into the world of firearms.  We offer hundreds of parts and accessories here at Aerospace Arms and hope you'll give us the opportunity to provide you a 5 star experience by supplying some of the parts and accessories for your next (or first) build!