Some more developments. There are three types of 40mm grenade fuse:
Contact. This is the simplest type. It just explodes as soon as it hits the ground (or wall etc.). Very accurate
Air burst. The grenade jumps up after hitting the ground, this can (in theory) do more damage, by hitting enemy hiding behind cover.
Timed. The grenade explodes after a set time, allowing it to bounce and travel further. The disadvantage is that it unpredictable where it will detonate.