Herrington Arms P320+5 Magazine ExtensionThis mag extension is made of light yet very strong aircraft grade 7075 aluminum. We prefer this material for magazine baseplates given the amount of wear and tear they see on the training range, in competition shooting, or on duty as a first responder. With the floor plate design that we implemented on our mag extensions, it makes installing them and changing the springs after extensive use easy for the end user. It works with 15, 17, and 21 round