Damage from underslung and vehicle mounted grenade launchers do not seem to produce major damage. One instance firing many grenades from a Hunter (name?) the grenades were falling on top of enemies and it took several hits to take down...some not at all. Seems as though the damage is not significant and splash damage is not as well.
- Legacy ID
I've been having this same issue. At one point it took 3 or 4 direct hits from a 40mm grenade launcher on the Hunter GMG to kill one infantryman.
I've also noticed that regular fragmentation grenades don't do much damage to players either. Two near/direct contact explosions were not enough to kill myself after literally hopping onto/standing next to them just before they explode.
On the vehicle showcase, I failed to kill infantry in the vehicle depot with 2 direct hits from the GMG on the stolen vehicle. It looked as though the grendades landed inside a meter of the two EI. A third shot finally took them down.