Mil-Spec Buffer Tube Kit

The mil-spec carbine buffer tube kit represents the foundational recoil system component for AR-15 builds, providing the essential interface between the lower receiver and adjustable buttstock. This complete assembly includes the 6-position buffer tube, carbine-weight buffer, carbine-length buffer spring, castle nut, and end plate—everything needed to complete the rear of the rifle. The mil-spec designation refers to the specific 1.14-inch outer diameter threading and geometry that ensures compatibility with true mil-spec stocks from manufacturers adhering to military specifications.

Understanding the distinction between mil-spec and commercial buffer tubes proves critical for successful builds. Mil-spec tubes feature slightly smaller outer diameter (1.14 inches vs. 1.17 inches commercial) and employ a different thread pitch, making them incompatible with commercial-spec stocks despite similar appearance. The vast majority of quality manufacturers produce mil-spec stocks and buffer tubes, making mil-spec the de facto standard for serious builds. The 6-position adjustment mechanism allows precise length-of-pull customization from approximately 10 to 13 inches, accommodating shooters of different statures and those wearing body armor.

Complete buffer tube kits provide value and convenience for builders, eliminating the need to source individual components and ensuring all parts work together properly. The included carbine buffer (typically 3.0-3.2 oz) and standard carbine spring suit most unsuppressed AR-15 configurations, though shooters running suppressors will want to upgrade to H2/H3 buffers and enhanced power springs. Quality varies significantly between manufacturers, with reputable brands offering properly staked castle nuts, precisely machined tubes, and springs that resist taking a set over thousands of cycles.