Couldn't you make the gun do a rediculously low amount of damage to still award the kill?
I could help with the issues.I could also tell you how to fix them.
I'm not really a scripter, but couldn't you make it do very little damage, launch them in the air, then it makes their model (and corpse i would guess) invisible and launches them down, awarding the player the kill?
If that were the case then effects from the invisible corpse disappearing (smoke) showing up would be the problem.
How so?