There seems to be some oddness with the type 115 50cal. Soliders with level IV or V helmets (like the Viper helmet) can survive multiple (6) shots to the head from this at close range. However, I am able to destroy the y-32 xi'an in a few (4-6) shots with this weapon. It also penetrates the glass and can kill the crew, which seems to be the quickest way to make the xi'an explode.
Note that this is not the pilot death bug causing the explosion though; if I kill the crew with the Lynx the aircraft does not explode. It also takes a LOT more ammo (30-40ish) from the Lynx to make the xi'an explode than it does from the type115. The 6.5mm from the type 115's main barrel also kills a solider with a level IV helmet in one shot. Curiously, the 6.5 does not penetrate the xi'an glass while the 50cal does.
So which is meant to have better penetration? My assumption here is that the type 115 50cal has some sort of unique property vs. vehicles.