Now you can convert your existing ELMS or ELMS PLUS Laser Cartridge to use in your 12GA shotgun! The ELMS 12GA shotgun Back Cap is compatible with the following caliber ELMS or ELMS PLUS Laser Cartridges; 9MM – 40S&W – 380ACP – .357SIG – 10MM – MAKAROV Simply unscrew the existing Back Cap from your cartridge body. Be careful to keep the batteries inside the cartridge body itself. Next, place the original Back Cap into the ELMS case for safe keeping and later use. Finally, screw your new 12GA Back Cap onto the cartridge body and firmly depress the rubber strike pad with a ball point pen to verify that the laser is firing. Be advised that the ELMS 12GA Back Cap is NOT compatible with any Laser Cartridge other than the ELMS caliber designations listed above. This Back Cap will not fit a GEN2 brass color laser cartridge.