AR15 Lower Receiver: Components and Importance

Project ar15 Sep 19, 2023
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Ar15 Lower Receiver Main Components

Why is the AR-15 Lower Receiver so Important? Explore Its Key Components and Legal Significance

The AR-15 lower receiver is at the heart of America's most iconic rifle platform. This small but crucial part plays a pivotal role in the functionality and customization of the AR-15 rifle. In this article, we will break down each of the major components of the AR-15 lower receiver, including the trigger/hammer, pistol grip, buffer tube and spring, safety selector, magazine catch, bolt catch and buttstock. We'll also discuss the materials commonly used in crafting these lowers and unravel the unique legal status of this component.

AR15 Trigger/Hammer Assembly

The trigger and hammer assembly is one of the most important components of the AR-15 lower receiver consisting of the trigger, hammer, hammer spring and disconnector. And of course the pins to secure it into place. It is responsible for initiating the firing sequence of the rifle. When the trigger is pulled, it releases the hammer, which strikes the firing pin, ultimately igniting the cartridge's primer and firing the round. The quality of this component greatly affects the rifle's accuracy and rate of fire.

AR15 Pistol Grip

The pistol grip is the handle located at the rear of the lower receiver, where the shooter's hand rests. It provides a comfortable and ergonomic hold on the rifle. Pistol grips come in various shapes and sizes to accommodate different shooting styles and hand sizes. Some even offer storage compartments for small tools or extra rounds.

What is the Importance of the AR15 Buffer Tube and Spring?

The buffer tube and spring are part of the AR-15's cycling system. When a round is fired, the bolt carrier group (BCG) cycles backward, and the buffer spring compresses. The buffer tube facilitates the rearward movement of the BCG and the spring returns the BCG forward. It will also absorb and dampen some recoil, allowing for quicker follow-up shots and improved control. The buffer tube also houses the rifle's buffer weight, these come in various weights to tailor the rifle's performance.

AR15 Safety Selector, Your Choice of Course.

The safety selector is a small lever located on the side of the lower receiver near the trigger. Generally, there are two positions: Safe and Fire. If the rifle is capable of full-auto or burst fire the safety selector has three positions: safe, semi-automatic, and automatic. The safety selector is a critical safety feature, ensuring that the rifle can only be fired when intended. These come in many aftermarket variations to accommodate user preference. Ambidextrous safeties have become a popular option, allowing operation by both Right and Left handed shooters. 

AR15 Magazine Catch/Release

The magazine catch/release is a critical component of the AR-15 lower receiver that allows for the insertion and removal of magazines. It consists of a button or lever, often located on the right side of the lower receiver, just beyond the trigger guard. When the shooter presses the magazine release, it disengages the magazine from the rifle, allowing for quick and efficient magazine changes.

This component is vital for maintaining the rifle's functionality and ensuring that it can feed ammunition reliably. It is designed to securely hold the magazine in place during firing while also providing a user-friendly mechanism for rapid reloading. 

What is an AR15 Bolt Catch/Release

The bolt catch/release is another integral part of the AR-15 lower receiver. It serves multiple functions related to the rifle's operation. When the last round is fired from the magazine, the bolt catch holds the bolt carrier group (BCG) in the open position, indicating that the rifle is empty. This is a crucial safety feature that signals to the shooter that it's time to reload.

Additionally, the bolt catch can be manually engaged to lock the bolt carrier group back for cleaning or inspection. To release the bolt, the shooter simply presses the bolt catch/release button or lever, long reffered to as the "ping-pong paddle", allowing the BCG to close, chambering a round if a loaded magazine is present.

AR15 Buttstock

The buttstock is attached to the rear of the lower receiver and provides support for the shooter's shoulder. AR-15 buttstocks come in various styles, including fixed, collapsible, and adjustable. The choice of buttstock can impact the length of pull, comfort, and overall handling of the rifle.

Materials Used in Ar15 Lower Receivers

Lower receivers can be crafted from various materials, with the most common being aluminum and polymer.


Most AR-15 lower receivers are made from forged or billet aluminum. Forged receivers are created by hammering aluminum into a mold, making them strong and durable. Billet receivers are machined from a solid block of aluminum, allowing for more intricate designs but are generally heavier.


Polymer lowers are lightweight and cost-effective. They are a popular choice for budget or lightweight build projects. While not as robust as aluminum, modern polymer lowers are surprisingly durable and resistant to the elements.

What's so Special About the AR15 Lower Receiver?

One of the most intriguing aspects of the AR-15 lower receiver is its unique legal status in the United States. Under federal law, the lower receiver is considered the "firearm" of the AR-15 platform. This is the serialized part that requires a background check and must be purchased through a licensed dealer. The other components, such as the upper receiver, barrel, and accessories, can be bought without these restrictions.

The AR-15 lower receiver is a remarkable piece of engineering that plays a vital role in the functionality and customization of one of the most popular rifles in the United States. Understanding its major components, materials, and unique legal status is essential for both enthusiasts and those entering the world of firearm ownership. Whether you're building your AR-15 from scratch or simply looking to upgrade, the lower receiver is where it all begins.