I often try to headcrab people involved in grapples.. seems like it should be easy, right? But I don't think I've EVER done it successfully. Am I just missing, or is it impossible?
It is possible just difficult. I've headcrabbed assassins who are grappling Jack Bots before. The thing is that their model does have the hit box where it shows the model and since many grapples have intricate animations (most noticibly the assassins) it can be difficult to time your throw to have the bomb connect with your target.
I assume you went as close as possible to get it just right? Well one thing I've learned is to sure as hell keep a slight distance or it'll simply land on the other side, though I'm pretty sure you shouldn't worry to much about the specific position they're in, even if it catches the guy's leg, it'll fly to side of his face! Anywho, it's possible
You can even do it solo - level charge up to 3, activate charge and bomb at same time while facing someone and the bomb will land on them during your grapple. Detonate bomb once grapple ends and enjoy the ultimate satisfaction of a charge-crab.
http://www.youtube.com/watch?v=j5rQtNx4Eew Awwwww yeah! Also; http://www.youtube.com/watch?v=YFS50wrE6Uc Charge 2. Be warned, Awpteamoose says something preeeeety nasty in the background.
It's very possible. try it out on a gunner for proof, its pretty damn hard to miss gunners and tanks, the other classes take a bit more finesse.
Yeah that's xbox, where the game aims for you. You can do it on PC but it is more or less a crap shoot.
