Hey mate, I'm gonna say that this achievement is definitely NOT accumulative, because I have loaded MANY levels where there are either infinitely re spawning enemies (Nosalises in Cursed) or just a lot of enemies in general (Lurkers in Defense and soldiers in Frontline) and I still haven't got it. I even counted the amount of grenades that I threw that got kills and after 15 it didn't pop. People have said that Multikills (e.g. throw nade into group of soldiers) count towards this, but it doesn't seem to be helping me at all. I have to do another playthrough soon to get Sticks Like A Bur, Ka-Boom, and Weaponsmith.
P.S I will also say that the Ka-Boom achievement is NOT accumulative either because I still havent got it. I'll post in when (and if) I get it on my next playthrough. Please post if you have any luck yourself!
I also read in another thread that people have gotten this achievement by throwing grenades at the masses of rats in the Ghosts level, at the bit where you enter the room and there is green glowing stuff on the ground and lots of rats, right before you open the door and the dead body falls out.
Last edited by Batmann77; 10-18-2011 at 11:51 AM.
Reason: Additional Information