I am recommending the following, as this is how I'm going to tackle this trophy.
Sidearm: M1911
Game-Type: Conquest
Map: Devastation or Rotterdam
Note: In Conquest, if the opposing team controls most of the flags the round will end sooner. This makes it more difficult. Since these rounds are usually about 30 minutes though, there's plenty of time to bag this one. Happy Hunting! ;)