Manufacturers build the AR-15 platform using a combination of aluminum alloys, steel components, and synthetic polymers. They apply various protective finishes and surface treatments to improve corrosion resistance, durability, and operational reliability. Since engineers originally developed the rifle in the 1950s, designers and manufacturers have continually refined these materials and coatings to meet military, law-enforcement, and civilian requirements.

Receiver Materials

Most manufacturers produce the upper and lower receivers of AR-15 rifles from 7075-T6 aluminum alloy because it offers a high strength-to-weight ratio while remaining relatively easy to machine. Manufacturers typically create receivers through forging or billet machining.

Forged receivers: Manufacturers press heated aluminum into a die to create the receiver shape. This process strengthens the grain structure and improves overall durability.
Billet receivers: Machinists mill these receivers from a solid block of aluminum using CNC equipment. Designers often incorporate unique external shapes or features while maintaining standard internal dimensions.

After machining, manufacturers almost always apply Type III hardcoat anodizing (MIL-A-8625 Type III) to aluminum receivers. This electrochemical process forms a thick aluminum oxide layer that increases wear resistance and corrosion protection. Companies most commonly dye this finish black, though they may also produce it in colors such as flat dark earth or olive drab.

Barrel Materials

Manufacturers typically produce AR-15 barrels from chrome-molybdenum steel (commonly 4140 or 4150 steel) or stainless steel alloys such as 416R. Many military-pattern rifles use chrome-moly steels because they withstand sustained firing and mechanical stress. Precision-oriented rifles often use stainless steel barrels because machinists can produce consistent rifling that may enhance accuracy.

Manufacturers also apply several internal and external finishes to barrels:

Chrome lining: Electroplaters deposit a thin layer of hard chromium inside the bore and chamber to improve corrosion resistance and reduce wear.
Nitride (ferritic nitrocarburizing): Technicians use heat treatment to diffuse nitrogen and carbon into the steel surface, creating a hardened and corrosion-resistant layer.
Phosphate coating (manganese or zinc phosphate): Manufacturers apply this matte finish to protect the exterior surface and improve lubricity.

Bolt Carrier Group

Manufacturers produce the bolt carrier group (BCG)—including the bolt, carrier, cam pin, firing pin, and retaining pin—from hardened steel alloys that withstand repeated high-pressure firing cycles.

Common materials include:

Carpenter 158 steel or 9310 steel for the bolt
8620 steel for the bolt carrier

Manufacturers heat-treat these components and apply surface finishes to improve durability and function. Traditional BCGs use manganese phosphate (parkerizing), which retains lubrication effectively. Many modern manufacturers instead apply coatings such as nickel-boron, nickel-teflon, black nitride, or diamond-like carbon (DLC) to reduce friction and simplify cleaning.

Small Steel Components

Manufacturers produce other functional components—including the barrel extension, gas block, gas tube, buffer system parts, and trigger components—from carbon steel or stainless steel. They apply several finishes to protect these parts and improve performance, including:

Phosphate coatings
Nitride treatments
Black oxide finishes
Hard chrome plating (used in some components)

These treatments increase corrosion resistance and improve long-term mechanical durability.

Polymer Components

Modern AR-15 rifles also incorporate glass-reinforced polymer parts to reduce weight and manufacturing cost. Manufacturers commonly produce the following components from polymer:

Pistol grips
Buttstocks
Handguards
Magazine bodies

Manufacturers typically injection-mold these components from engineering plastics such as glass-filled nylon. They often texture the surfaces and mold them in a variety of colors to improve ergonomics and provide aesthetic options.

External Protective Coatings

Some manufacturers apply additional external coatings to improve environmental resistance and appearance. Common examples include:

Ceramic-polymer coatings (such as Cerakote)
PTFE-based coatings
Powder coatings

These coatings can enhance corrosion resistance, reduce infrared signature, or provide camouflage coloration.

Evolution of Materials and Finishes

Since the introduction of the AR-15 platform, designers and manufacturers have continuously refined its metallurgy and surface treatments. Early developers added chrome-plated chambers and later chrome-lined bores to address reliability issues in humid environments and under heavy firing schedules. More recently, manufacturers have adopted nitrocarburizing and advanced coating technologies to improve service life and simplify maintenance.

Today, manufacturers choose materials and finishes according to the rifle’s intended role—whether military service, competitive shooting, or recreational use—while balancing durability, cost, and weight.