The KNS AR/MCX Stock Adapter is a modular solution for shooters running non-standard AR platform uppers or alternative receiver designs that don't need a traditional buffer tube to function. If you're building a rifle around a PSA, KP15, or similar design where the carrier and buffer assembly don't mechanically protrude past the receiver ring, this adapter lets you swap in Picatinny-compatible stocks—like the SIG MPX folding stock—instead of relying on AR15-pattern buffer tube hardware. It's a clean way to add adjustability and compactness without redesigning your lower receiver.

The adapter kit consists of two components: an externally-threaded plug that screws into your firearm's threaded buffer socket, and a rail section that slots into that plug. A single hex-socket bolt and lock washer secure everything together. The design is straightforward and field-strippable, making it easy to swap stocks or transition to different configurations depending on your mission.

This adapter is NOT compatible with standard AR15 lowers paired with MCX uppers, and it requires that your carrier and buffer tube don't extend beyond the receiver ring. If you're adapting this to an AR15 lower, you'll need a take-down pin that operates without a spring or detent—a less common part that some builders source separately. Think of this as a specialized tool for the tinkerer: it opens doors for otherwise incompatible setups but demands that you understand your platform's geometry before ordering.