MWx Each time a friendly operative makes a shooting attack with this weapon, in the Roll Attack Dice step of that shooting attack, for each critical hit retained, inflict x mortal wounds on the target. x is the number after the weapon's MW, e.g. MW3.
Lethal x Each time a friendly operative fights in combat or makes a shooting attack with this weapon, in the Roll Attack Dice step of that combat or shooting attack, your attack dice results of equal to or greater than x that are successful hits are critical hits. x is the number after the weapon's Lethal, e.g. Lethal 5+.