The CMMG AR-15 Gunbuilder’s Lower Parts Kit (brand part no. 55CA601) gives builders every small part needed to finish an AR-15 lower receiver in one box. Made by CMMG, the kit includes the bolt catch with roll pin, bolt catch plunger and spring, trigger and hammer retaining pins, safety selector with detent and spring, magazine catch with spring and release button, pivot and takedown pins with detents and springs, and the buffer retainer with spring. That covers every detent and pin a home or shop build needs beyond the trigger group and grip, saving you from tracking down a dozen individual small parts. Quality springs and detents matter for a lower that runs smoothly for years, and CMMG builds this kit to the same standard as its complete rifles.

Key Specifications

• Includes a bolt catch and roll pin for capturing the bolt carrier group.
• Includes the bolt catch plunger and spring for reliable function.
• Includes trigger and hammer retaining pins to complete the fire control group installation.
• Includes a safety selector detent and spring for correct safety tension.
• Includes the magazine catch, spring, and release button assembly.
• Includes pivot and takedown pins with detents and springs for the upper-to-lower connection.
• Includes the buffer retainer and spring to secure the buffer tube.
• Built specifically for the AR-15 platform.
• Weighs approximately 0.2 pounds.

Frequently Asked Questions

What does this kit include? Every small pin, detent, and spring needed to finish an AR-15 lower beyond the trigger group and grip.

Is this kit compatible with standard AR-15 lowers? Yes, it is built for the AR-15 platform and standard mil-spec lower receivers.

Buy the CMMG AR-15 Gunbuilder’s Lower Parts Kit

Finish your build with quality small parts instead of hunting down a dozen separate pieces. Order it from our Lubbock, Texas gun shop for fast, insured shipping, and browse our full selection of AR lower parts kits.