Warhammer 40,000: Inquisitor - Martyr

This achievement is for using ONLY grenade type items to kill 1000 enemies. These include:

Frag Grenade
Stun Grenade
Delayed Fuse Grenade

These are the only belt items that will count toward this achievement. Items that will NOT count include:

Digital Weapons
Stun Mine
Remote Mine
Any type of Shield, Deflector, or Refractor item.

The best way to work toward this is to not go out of your way to work on it. Just play through the game normally. You will constantly come across large groups of the small horde enemies like Gobblers, etc. Just toss a grenade at them any time you encounter these groups and you'll unlock this very quickly.