START A NEW 80 LOWER BUILD WITH 80% ARMS

Buying Guide: 80% Lower vs. Stripped Lower

Why choose an 80% build over a standard gun store purchase? Here is the regulatory breakdown:

Why 80 Percent Arms Leads the Industry

Builders trust us because we do not outsource. We do not private label. We do not play games. Every 80 percent lower we sell is machined in the USA from premium billet aluminum on state-of-the-art CNC equipment. Our tolerances are strict. Our QC is real. And our parts are built to last long after cheaper cast or foreign receivers fail.

The Anatomy of a Billet Lower

Not all receivers are created equal. We engineered our billet 80 lowers with enhancements you won't find on standard mil-spec forged parts:

• Integral Trigger Guard: Machined directly into the receiver for added strength and glove clearance. No more broken trigger guard "ears."
• Flared Magwell: A wider, chamfered opening allows for faster, more intuitive reloads under stress.
• Threaded Bolt Catch Pin: We replaced the frustrating roll pin with a threaded screw for easy assembly.
• Reinforced Buffer Tower: Added material in the critical stress point where the buffer tube meets the receiver.

The Machining Requirement

An 80% receiver is not a firearm until it is machined. This process involves removing the aluminum from the fire control pocket and drilling the necessary selector and pin holes. Once this material is removed, the receiver is legally considered a firearm.

Note: In compliance with ATF Rule 2021R-05F, we do not sell jigs or tooling fixtures. Our lowers are sold as standalone receiver blanks for use with your existing tools or third-party equipment.

AR15 80 Percent Lowers: Strong, Precise, and Built for Real Use

Our AR15 80 lowers are cut from high grade billet aluminum for the cleanest machining surface and the strongest finished receiver. These lowers are built for builders who care about alignment, geometry, and long-term durability.

Platform Compatibility Matrix

One Lower, Infinite Calibers

The beauty of the AR platform is modularity. Once you finish your 80 lower, it is the legally serialized part. You can swap upper receivers to change calibers in seconds. Our AR-15 lowers support:

• .223 Remington / 5.56 NATO (Standard)
• .300 Blackout (Use same magazines/bolt)
• 6.5 Grendel (Long range)
• .458 SOCOM (Heavy hitter)
• .22 LR (With conversion kit)

Material Science: Why We Choose 6061-T6

When choosing the best 80 lower, the alloy matters. We optimize our receivers for home builders.

6061-T6 (Our Standard): This is the ideal alloy for 80% builds. It offers the perfect balance of high strength, excellent corrosion resistance, and machinability. 6061 is significantly easier to mill with a router than 7075, which means your end mills last longer, your cuts are cleaner, and you are less likely to experience tool chatter or breakage during the process.

A Note on 7075: While 7075-T6 is a harder alloy, it is brittle and much more difficult to machine at home without industrial coolant systems. For a reliable, high-strength home build that is enjoyable to machine, 6061-T6 Billet is the superior choice.

Polymer vs. Aluminum: Which Should You Trust?

Many budget sites sell polymer 80 lowers. While polymer is fine for pistol frames (like our GST-9), we strictly recommend Aluminum Billet for rifle lowers. Polymer rifle lowers often crack at the buffer tower extension due to the recoil impulse of the bolt carrier group.

Regulatory Note: In accordance with ATF Final Rule 2021R-05F, the GST-9 Modular Frame is classified as a firearm and must be shipped to a local gun store (FFL) where you will complete a background check before pickup.

Comparison: Billet vs. Forged vs. Cast

Raw vs. Anodized: Making the Choice

We offer lowers in two finishes:
Raw (In-the-white): These are unpainted aluminum. Perfect if you plan to do a custom Cerakote job or want to practice polishing.
Type III Hardcoat Anodized: This is the military standard (Mil-A-8625). It creates a super-hard, corrosion-resistant surface layer that protects the aluminum from wear and scratches. If you want a black rifle that lasts, choose Anodized.

Universal Jig Compatibility

Our receivers are precision-engineered to mil-spec dimensions, making them universally compatible with standard router jig systems available on the market, including legacy Easy Jig models and other third-party fixtures.

Compliance Notice: To comply with ATF Final Rule 2021R-05F, we have discontinued the sale of jigs and tooling fixtures. Our lowers are sold as standalone receiver blanks for use with your existing tools or third-party equipment.

Checklist: What You Need to Finish Your Build

When you buy an 80 lower, you are buying just the receiver blank. To complete the firearm, ensure you have the following:

• 80% Lower Jig: (Must be sourced from third-party tooling providers)
• Tooling Kit: End mill and drill bits (Sourced separately)
• Router: A standard handheld router (Dewalt, Makita, or Bosch)
• Lower Parts Kit (LPK): Triggers, springs, and pins
• Buffer Tube Kit: Buffer tube, spring, weight, and stock
• Complete Upper Receiver: Barrel, handguard, and bolt carrier group

Why Builders Searching for “80 Lower” Choose Us

The “80 lower” keyword is one of the most competitive in the firearms industry, and builders consistently choose 80 Percent Arms. Why? Because when accuracy matters, you need a receiver that won’t bend, crack, or shift during machining. Our parts are American made, Billet construction (not cast), and held to strict tolerances.

Home Building Legality and State Restrictions

Building a firearm at home from an 80 percent lower is generally legal for personal use. However, due to changing laws, our products are restricted in the following states and jurisdictions: CA, CO, CT, DC, DE, HI, IL, MA, MD, NJ, NV, NY, OR, VT, and WA.

LEGAL DISCLAIMER: This list is not comprehensive and is not actively updated. Please be sure to check the laws in your local jurisdiction. Laws regarding the purchase and possession of unfinished receivers change frequently. It is 100% the responsibility of the customer to research and understand their specific state, county, and local laws before ordering. 80 Percent Arms is not responsible for the legal ramifications of your purchase or possession of these items.

Troubleshooting Common Mistakes

For the best results with your build, ensure you use proper aluminum cutting fluid to extend tool life and maintain consistent router speeds to prevent chatter.

Glossary of 80% Terminology

Receiver Blank: The technical ATF term for an 80% lower.
Fire Control Group (FCG): The trigger, hammer, disconnect, and safety selector.
Detent: Small pins used to hold takedown pins and selectors in place.
Jig: A fixture used to hold the lower in place and guide the drill/router during machining.