Incendiary ammo works for this. If anyone is having trouble saying "incendiary ammo" to the Kinect, say "in-send-e-air-e ammo". I've heard several of my friends pronounce it like the word incinerate. That won't work, you have to enunciate the "d" and "i" in the word. Hope this helps save some frustration.
It must be the player character's abilities that you use. It's not like ME2 where you could command your squadmates and get progress. So either Shepard or MP characters - and incendiary ammo does work (I got the achievement in less than 2 hours on MP that way)
So either Shepard or MP characters - and incendiary ammo does work (I got the achievement in less than 2 hours on MP that way)