Here is a list of the weapons you need to complete this achievement all you need to do is get one kill with each weapon,
Shotgun,
Frag grenade,
Lancer,
Boomshot,
Scorcher,
Longshot,
Ink grenade,
Torque bow,
Mulcher,
Mortor,
Hammer of dawn,
Gorgon pistol,
Boltok pistol,
Cog pistol,
Hammerburst.
An easy way to achieve this would be to set up a private game vs. a friend/bot/second controller then customise all the weapons for the ones you need and get your kill with it.