A rail mountable device may be provided that is configured to be secured firmly to a rail, such as a rail on a firearm, and released easily from the rail. In one example, the rail mountable device may include a rail clamp that includes first and second rail-engaging surfaces of corresponding first and second ramp members and a cross member that, in response to rotation of a screw, move toward or away from the longitudinal faces of the rail of the firearm to secure or release the rail mountable device to or from the rail. Additional embodiments and related methods are provided.