FN Herstal has developed a 40mm grenade launcher sighting system called the FN Fire Control Unit (FN FCU).

FN FCU mounted on FN SCAR

The FCU is mounted on a picatinny rail above the launcher. A laser range finder calculates the distance to the target and a clinometer measures the angle/elevation to the target. A ballistic computer then calculates the required angle of fire and a red dot sight is moved to point at the correct aiming point. The cant indicator will tell the operator if the weapon is canted and require realignment.

As you can see in the photo, iron sights and/or optics can still be used. This system could be used on standalone launchers or under-barrel launchers.

It looks good in theory, as do other 40mm laser sighting systems, but I have heard from various readers that one system, the H&K M320 laser sighting system, is not very useful in the field and I wonder if the problems with that system also apply to the FN FCU. Back in 2008 Sean wrote …

I was a grenadier in the Army and deployed to Afghanistan in ’06 where they tried to foist that sight on us, and to a man, we hated it. firing a 203 is easy; couple of trips to the range, you’re good to go. it’s just about learning angles and distances and generally being comfortable with the weapon. once you’re there, you can fire, as a guess, 20 or so accurate rounds a minute. that sight cuts that in half. i don’t know much about the 320, but that sight has got to go.

Sean elaborated here.