I wanted to install a full-size weapon mounted light on my Bul SAS II UL Viper, but the picatinny rail is too short for most full-size lights to mount to, so I made my own custom rail key for a Streamlight TLR-1 HL (made from two other non-common rail keys that come with the light) to allow it to securely mount to the shorter picatinny rail of the Viper and position the light very close to the front of the trigger guard.