Unreal Tournament III

The "Gunslinger" award is earned for getting 15 kills with the Enforcer in a single match.

Suggested Setup
Gametype: Deathmatch
Map: Morbias Arena
Mutators: Speed Freak, Weapon Replacement (Rocket Launcher to Enforcer)

All of the weapon related trophies that are played on Morbius Arena basically function the same. Set the match to 20 kills so that you can work toward Get a Life at the same time, then simply play the matches to 20 kills. With Speed Freak on and Novice bots you can run back and forth from one end of the map to the other and take out many people very quickly. Once you've made it through 10 matches switch the date forward one and move on to the next trophy.