Made from Heat Treated 410 Stainless Steel for Ultimate Durability. MBX Built a Specific Competition Ready Magazine to Ensure that it sits at the correct Height within the frame from Bul Armory. This puts the bullet in the optimal position to provide smooth, seamless feeding, and reliability. MBX tubes are designed to be Competition Ready with exclusive features to meet the highest demands for today’s shooters. 126mm 9mm/.38 Magazines hold 20-21rds – 126mm .40cal/10mm Magazines hold 18-19rds – 141.25mm 9mm/.38 Magazines hold 23-24rds – 141.25mm .40cal/10mm Magazines hole 20-21rds – MBX tubes are designed exclusively to work with MBX Followers, Springs, & Basepads. – Witness Holes on the rear of the tube to indicate round count for all tubes.