first of all...welcome to the forums!
second of all, there are detailed tutorials and a pretty extensive forum, i would recommend reading the tuts, and using the search fuction of the forums.
as for your question, the easiest method to do a 1 shot kill weapon is changing the projectile of the orginal gun to something more destructive(a gun that is known to do 1 shot kill).
If you were doing this for BF42, I would recommend the bazooka protectile, knowing that it has a pretty good 1 shot kill.
The second thing is do you want the splash damage.
If you do, you will change the projectile of the current weapon to the bazooka projectile. If you do not want splash damage, you will want to change the material number to the same as the bazooka of the current projectile of the weapon.
The material number defines the projectiles destructive ability with other objects and what location of the object (ie...head, torso, legs...etc...).
I dont want to give you the code right away. First read the tuts and forum an start working on the code and post back...and chances are you will get it right.
good luck
