In the instruction booklet it say things like: bazooka 50 dmg max, grenades 50 dmg max, mines 45 dmg max, blowtorch 50 dmg max, pneumatic drill 50 dmg max, airstrike 70 dmg max, bunker buster 40 dmg max.

The max that I succed doing with these weapons are: bazooka 48, grenades 47, mines 43, blowtorch/pneumatic drill 45, airstrike 54, bunker buster 38.

Are the max dmg possible? Did anyone of you succed doing it? How can it be done?

You have to get the shot perfect to get the max damage. Aim straight up while sitting on a worm's head and just tap the fire button so the grenade stays on his head. It'll be the max damage.

putting the grenade on the head of the worm usualy do 45 dmg sometimes 46 or even 47 but I've never seen 50 dmg

I imagine that could be because the exact centre of a worm, which is used in determining the damage, is actually inside of it.

On Worms Armageddon, you can get very close to the maximum damage of each weapon by detonating it while it's inside a worm's collision mask. The easiest way of getting there is to either jump into a worm from below while it's standing on a slope or rope knock it, and then plant an explosive once the two worms are standing in the same spot.

I can't know whether that works in Open Warfare games because I don't have them handy, but it should give you a general idea of what needs to be done. ;)

a good way to get full damage with the airstrike is to put an electromagnet on attract and fire when a worm is there