The Stern Defense SD BU9 9mm Complete Bolt Mag-Phosphate is a dedicated bolt carrier group engineered for AR-15 and AR-9 builds that run Glock or Colt SMG magazines. Machined from durable 8620 AISI steel and finished in a mag-phosphate coating, it is designed to handle the heat and fouling of high-volume pistol-caliber shooting while maintaining smooth, reliable cycling.

This bolt arrives fully assembled with its firing pin, springs, retaining pin, and custom 4140 billet extractor already installed, making it a straightforward drop-in choice for Mil-Spec and Glock-pattern upper receivers. It works with standard AR-15/M16 charging handles and is compatible with popular upgrades such as single-stage short-reset triggers, JP silent capture springs, Law Tactical folding stock adapters, and Echo triggers. Ideal for range use, PCC competition, and training-focused AR-9 builds, the SD BU9 reflects Stern Defense’s focus on practical design and consistent performance.

Key Features:

• Manufacturer: Stern Defense
• Model: SD BU9
• Caliber: 9mm Luger
• Condition: New
• Weight: 15.5 oz
• Length: 7.7 in
• Unique Features: Glock cut, custom 4140 billet extractor, compatible with JP silent capture spring, Law Tactical folding stock adapter, and Echo trigger