I killed a man

Hi,

I killed the frontline dwarf fighter of our party in 1 shot.

In the opening shot of the party's full frontal assult, they took more than their max health dmg from a x4 cannon crit. What would have been 15 dmg became 60 dmg.

Once they were in this situation, there was nothing they could have done, and they took it well and everything, but I felt bad. It got me thinking...

What amount of insta-gib do you guys consider acceptable risk?