It's a pretty good way to prepare for low-light encounters with bad guys, too. Here are some tips to ensure you mount your weaponlight properly from Huntington Beach, CA, police officer and SureFire Institute Lead Instructor Bill Murphy.
1Mount the light on the bottom rail section of your fore-end. Gases coming from the barrel rise and can obscure the beam from a top- or side-mounted light. Also, if using most vertical foregrip/light units, there will be no shadow from the barrel.
2Bottom-mounted lights allow the use of a traditional sling, as the light will be snug against a right-handed shooter's body. With a light mounted on either side, a single-point sling is needed to avoid damaging the bulb when moving through tight spaces.
3Mount the light as close to the receiver as possible, which helps balance the weight of the light between the hands. Extra weight—even the few extra ounces added by a light—can lead to a tired support arm, especially if those ounces are hanging off the fore-end in front of your weak hand.
4Ensure the light does not interfere with the magazine. Too close to the mag well can make changing magazines difficult. Plus, you don't want to hit the light during a mag change, which can slow down the reload and damage the light.