Bungie need to change the quest. It is impossible for average or below average pvp players to aquire this weapon
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Then just cheese it like the majority of the community did. If you have Last Word equipped at the end of a match and your team wins, you are rewarded 3% just do this 34 times. You could also play smart and adjust to the strengths of the weapon and get kills that way like i did and add that the xp from match wins.