In this day and age, I'm not sure that I would want to be firing anything less than the main armament at something that could shoot back and kill me. A ranging burst with a MG would give away your position, and if the other guy got lucky, he would hit you well before you went through all the procedures inherent in calculating how far the MG rds were hitting, if at all.
There are other methods available that are passive (as opposed to active, which the laser is.... we have laser warning detectors, and I'm sure any worthy Banana Republic army does too. When I taught gunnery, I told guys to think about aiming away from a target, but at the same approx range before lasing.... but if you are doing a quick engagement, lase for center of visible mass, and once the gunner reports range, if it seems close enough for gov't work, give executive to fire, and then make corrections (if neccesary)). Anyway, there are optical methods for determining range, which use the mil scale (1 mil at 1000meters equals 1 meter). So, if you knew that a vehicle was 2.5 meters wide, and it is 2.5 mils wide, you know it is at 1000m, and so on.
Al