Psyker (Mastery Level 1)

Force weapons have the same effects as power weapons, but also confer to the wielder one additional psychic power, used in close combat, that can instantly extinguish the life force of any opponent. 

Roll to hit and wound as normal, allowing any invulnerable saving throws the victim might have. The psyker may then take a Psychic test to use the weapon’s power against any one opponent that suffered an unsaved wound by the weapon in that player turn. The normal rules for using psychic powers apply (remember that a psyker may normally use only one power per turn). If the test is passed, the enemy model suffers instant death, regardless of its Toughness value. This power has no effect against vehicles, models that are immune to instant death and any other model that does not have a Wounds value.