A system and apparatus for mounting accessory devices on projectile launching devices is described. Particularly, a mounting system for rangefinders which facilitates rotary movement of mounting elements about multiple axes and linear movement of mounting elements along multiple paths is described. In the case of a device for mounting rangefinders on shooting devices, the mounting device enables the position of the rangefinder to be fixed prior to mounting the rangefinder on the shooting device so that the rangefinder when mounted is aligned and calibrated to the viewfinder of the shooting device. This enables a user to compensate for the trajectory of a projectile over the range or distance between the user and the target.