You need to take someone from positive HP all the way to death with a single attack to trigger a violent death.
That means doing at the very least 101 direct damage to player characters (less to npcs). Theres not many small guns that can do this against an armored opponent, in fact i can only think of four:
- A good armor bypass critical from DKS or M1C
- Gauss rifle
- very close ranged pancor burst