80% Lower Compatibility Guide

You're ready to become an at-home gunsmith and build an AR-15 from scratch. But which receiver blank should you buy? 

This guide compares available AR-type 80% lowers, which calibers they work with, and other specifications you'll need to know before building.

New here? Read "What is An 80% Lower?"

Need to find the right lower parts kit? Read this LPK compatibility guide.

Types of 80% Lowers

Forged AR-15 80% Lower

The forged AR-15 80% lower is the first receiver blank to hit the market years ago. It's forged from 7075-T6 aluminum, like the typical retail-bought AR stripped lowers. It's the most affordable AR receiver blank that isn't made of polymer. The raw (non-anodized) version is the cheaper of the two, allowing you to apply a custom coating once fabricated. 

The black version is coated with a type III hardcoat anodized finish (mil-spec), so it'll match any retail AR-15 parts, upper, or built kit you pair it with. Although not fabricated nor functional, the forged AR 80% lower incorporates a finished, threaded buffer tube housing, front pivot and rear takedown pin holes, a machined magazine catch channel, and trigger guard mounts.

Forged AR-15 80% lowers available here.

Compatible with

• AR-15 upper assemblies and receivers.
• AR-15 buffer tube assemblies.
• AR-15 lower parts kits.
• AR-15 Rifle Kits.
• AR-15 80% jigs (sold elsewhere).

Available Calibers

• 5.56 NATO, .223 Remington
• 300 AAC Blackout
• 6.5 Grendel
• All other calibers compatible with 5.56/.223 lowers

Quick Specs

• Made of 7075-T6 forged aluminum.
• Raw or type III hardcoat anodized finish.
• The most affordable aluminum AR-type 80% lower.

Read the AR-15 Build Guide here.

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Billet AR-15 80% Lower

The billet AR-15 80% lower is an upgraded version of the forged lower. Both units function identically. The billet receiver is CNC-machined from 6061-T6 aluminum. It includes some upgrades, including an integrated trigger guard and threaded takedown detent and bolt catch pin holes. These threads make assembly simpler, since no roll pin punches are required.

Roll pins can be difficult to install or remove, and they require special punches, If you've assembled a lower receiver before, you know what we're talking about. This lower is also treated with a mil-spec type III hardcoat anodized finish. No raw version is currently available.

Billet AR-15 80% lowers available here.

Compatible with

• AR-15 upper assemblies and receivers.
• AR-15 buffer tube assemblies.
• AR-15 lower parts kits.
• AR-15 Rifle Kits.
• AR-15 Pistol Kits.
• AR-15 80% jigs (sold elsewhere).

Available Calibers

• 5.56 NATO, .223 Remington
• 300 AAC Blackout
• 6.5 Grendel
• All other calibers compatible with 5.56/.223 lowers

Quick Specs

• Made of 6061-T6 billet aluminum.
• Type III hardcoat anodized finish.
• Provides easier assembly w/ LPK.

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Billet LR-308 ("AR-10") 80% Lower

The aluminum .308-type 80% lower is the modern version of the military's AR-10 receiver. It's available as a billet unit machined with roll pin fittings or threaded fittings. It's also available in "in the raw" (uncoated) or with black type III anodizing.

Billet .308 80% lowers available here.

Compatibility: LR-308 vs. AR-10

Modern .308 ARs (including this receiver blank) are not based on the original ArmaLite AR-10. Instead, they're based on DPMS Panther Arms' LR-308 rifle. The LR-308's receivers are shaped a bit differently than the AR-10's receivers, and the upper receivers' barrels are also different. Otherwise, the DPMS .308 AR is functionally identical to the AR-10.

This lower uses mostly 5.56/.223 components in its lower parts kit, except for a few parts that are sized specifically for the larger caliber. The only parts not used from the AR-15's lower parts kit include the:

• Buffer
• Bolt catch
• Pistol grip
• Takedown pins
• Magazine catch

AR-10 vs. LR-308: What's Different?

Compatible with

• LR-308 upper assemblies and receivers.
• LR-308/AR-10 buffer assemblies.
• LR-308/AR-10 lower parts kits.
• LR-308 Rifle Kits.
• .308 80% jigs (sold elsewhere)

Quick Specs

• Made of 6061-T6 and 7075-T6 aluminum.
• Raw or type III hardcoat anodized finish.
• Roll pin fittings (7075) or threaded fittings (6061) available.

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AR-9 80% Lower

Pistol-caliber carbines have become popular among AR builders. Instead of modifying your 5.56/.223 lower with a 9mm conversion block, you can now build a dedicated AR chambered in 9mm with this lower. 

This AR9 receiver blank is a redesigned AR-15 lower with a modified magazine catch and magazine well that accept Glock magazines. It has a built-in 9mm ejector, designed to work with the 9mm bolt carrier group found in AR9 upper assemblies. It uses a standard AR-15 lower parts kit, including the same trigger, hammer, disconnector, safety, and springs. The same is true for AR-15 buffer assemblies. The 9mm only requires a heavier buffer.

9mm 80% lowers available here.

Compatible with:

• AR9 upper assemblies and AR-15 stripped uppers.
• AR9 one-piece "gas-less" bolt carrier group.
• Factory 9mm GLOCK pistol magazines.
• AR-15 lower parts kits and buffer tubes.

Quick Specs:

• Made from 6061-T6 billet aluminum.
• Type III hardcoat anodized finish.
• Factory-installed 9mm ejector.
• Factory-installed magazine catch.
• Integrated trigger guard.
• Uses standard takedown pins.

Read the AR-9 Pistol Build Guide here.

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Polymer 80% Lower

Polymer80's known for their 80% frames, but they also manufacture polymer AR-type 80% lowers. Polymer80's lowers feature all the same specifications and fitment as any "mil-spec" forged or billet lower. That means these polymer AR lowers use standard parts kits, buffer systems, magazines, and aluminum uppers. 

Polymer 80% lowers are popular because they're easier to fabricate: Cutting the fire control cavity and drilling the trigger pin holes requires less time and tooling. Polymer80 also provides a disposable 80% jig with the required tooling. The jig can be purchased with the lower.

If you're limited to using a small drill press -- or if you simply want to practice the process of machining an 80% lower in a safer, more affordable way -- a polymer lower is a great option.

Once fabricated, a polymer stripped lower is just as reliable and functional as any aluminum lower.

Shop polymer 80% lowers here.

Compatible with

• AR-15 upper assemblies and receivers.
• AR-15 buffer tube assemblies.
• AR-15 lower parts kits.
• AR-15 Rifle Kits.
• AR-15 80% jigs (sold elsewhere).

Available Calibers

• 5.56 NATO, .223 Remington
• 300 AAC Blackout
• 6.5 Grendel
• All other calibers compatible with 5.56/.223 lowers

Quick Specs

• Made of glass-reinforced nylon polymer.
• Stamped metal plate for optional serialization.
• The easiest AR-type 80% lower to machine.

Read the AR-15 Build Guide here.