A barrel seal activator is used on the 11-87 Super Magnum to improve performance when shooting 2¾” shells. You should remove the activator when shooting 3” and 3½” shells. The 11-87 Owner's Manual schematic has been updated with the most recent version of the barrel seal activator. In this diagram the barrel seal, piston seal assembly and barrel seal activator are shown in the proper positions on the 11-87 Super Magnum magazine tube. For complete instructions on assembly and disassembly of your firearm, please download the latest version of the owner's manual through the following link here.