Advanced Technology SHS1300: Fits: Most 12, 16 and 20GA and .410 pump shotgun barrels. Heatshields should not be used on Mossberg Mariner or Remington Marine Coat Shotguns. This will only fit if the barrel lug is more than 13.5 from the receiver. Note: Each Heatsheild should be custom fit. If you do not have the proper tools or do not feel comfortable fitting the heatshield to your firearm please enlist the services of your local gunsmith. ATI is not responsible for any damage caused by improper installation. Steel Formed Shotgun Heatshield. Elongated Cooling Slots for Maximum Dissipation of Heat. Easy Installation Simply Slide Over Barrel and Secure With Supplied Hardware. 13-1/2 Long