Rise Armament Lower Parts Kit 12003 LPK Without Fire Control Group

The Rise Armament Lower Parts Kit 12003 is a 20-piece AR-15 lower receiver parts kit designed for shooters building their own rifles. This kit gives you most of the components you need to assemble a complete lower receiver—everything except the fire control group, letting you choose your own trigger and hammer setup. It's built around mil-spec dimensions and proven materials, making it a solid foundation for a custom build, whether you're finishing a 80% lower, upgrading an existing rifle, or starting from scratch.

Rise Armament engineered these parts from industry-standard 8620 carbon steel—a nickel-chromium-molybdenum alloy prized for machining cleanly, resisting wear, and handling sustained shooting without fatigue. The takedown and pivot pin detents are yellow zinc for durability in those high-wear spots. Nearly all parts receive a black phosphate finish, an inert coating that stops corrosion at the steel surface rather than relying on oil alone. Black phosphate is the same finish you'll find on quality AR platforms across the industry; it's proven in hard use and keeps parts protected through range sessions and field work alike.

This kit includes everything from takedown pins and pivot pin detents to bolt catch assemblies, springs, selector, magazine catch, and buffer retention hardware. Since you're getting the parts without the fire control group, you have the freedom to build with a match-grade trigger, a lightweight single-stage unit, or whatever fire control suits your rifle's mission. The kit is scaled for 5.56 AR-15 patterns, keeping everything compatible and straightforward.

Key Features

• 20-piece kit covers receiver assembly except trigger and hammer
• Mil-spec dimensions for universal AR-15 lower receiver compatibility
• 8620 carbon steel construction—high-strength, wear-resistant alloy
• Black phosphate finish resists corrosion from extended shooting
• Yellow zinc detent pins for reinforced durability
• Complete takedown, pivot, and bolt catch hardware included
• Lets you select your own fire control group for customization

Specifications

Frequently Asked Questions

What's included in this lower parts kit—and what's not?

You get 20 pieces: both takedown and pivot pin detents, bolt catch assembly (plunger, spring, and roll pin), buffer retention hardware, trigger pins, safety selector, magazine catch (button and catch), and all associated springs and retaining pins. What's NOT included is the fire control group—the trigger and hammer—so you can source those separately based on your build preference.

Will this kit work with my AR-15 lower receiver?

Yes. This kit is built to mil-spec dimensions and is designed for standard AR-15 5.56 pattern lower receivers. The parts are compatible with any mil-spec lower, whether it's a standard forged receiver, billet, or 80% lower you've finished yourself.

What material are these parts made from?

Most parts are 8620 carbon steel—a nickel-chromium-molybdenum alloy that machines cleanly, resists wear, and handles continuous shooting. The takedown and pivot pin detents are yellow zinc for extra durability. Nearly all parts have a black phosphate finish, which creates an inert corrosion-resistant layer on the steel surface.

Can I use this kit for a bench build with no gunsmithing experience?

This kit gives you the small parts and hardware needed for lower assembly, but assembly still requires proper tools, knowledge of AR-15 mechanics, and careful attention to springs and detents. If you're new to it, consider consulting a detailed build guide or having an experienced gunsmith walk you through the process to avoid lost springs or incorrect pin placement.