Stern Defense SD-BU9 9mm AR-15 Bolt - 8620 Steel NIB/Mag Phosphate Hybrid

The Stern Defense SD-BU9 is a dedicated 9mm bolt purpose-built for AR-15 and M16 pistol caliber carbine platforms. It is machined from 8620 AISI steel and finished with a hybrid NIB (Nickel Boron) / Mag Phosphate coating, providing the hardness, corrosion resistance, and lubricity needed to handle the fouling and high cycle rates of a 9mm blowback AR setup.

The SD-BU9 drops into standard Mil-Spec upper receivers and is also compatible with Glock-pattern upper receivers, supporting both Colt SMG and Glock magazine-compatible 9mm AR builds. It functions with Colt SMG and Glock-pattern magazines, and it is fully compatible with standard AR-15/M16 charging handles so no specialty parts are required for installation.

Whether you are finishing out a new 9mm AR pistol or rifle build, replacing a worn PCC bolt, or refreshing a dedicated sub-gun upper, the Stern Defense SD-BU9 delivers a properly finished, high-strength bolt solution for your platform.