Mesa Tactical SureShell shtogun shell carrier for Remington 870/1100/11-87 (4-Shell, 12-GA) - Left SideMesa Tactical SureShell shell carrier mounts directly to the shotgun's receiver. That meant that each shell carrier had to be designed to fit a specific brand and model shotgun. Because of the basic design, only the backing plate/mounting bracket had to be changed. Note the cut-out area between the mounting screw holes that reveals the serial number on the 870's receiver..