Potato Masher Achievement
Kill 100 enemies with explosivesKills with grenades, mines and dynamite all count for this achievement. Hitting a grenade on an enemy webbing also counts, and any enemy eliminated by the ensuing explosion counts as well. This should unlock naturally over the course of your campaign playthroughs if you use your explosives wisely.
During Mission 3, 'Kaiser-Friedrich Museum', after you acquire the Mosin Nagant rifle, exit the building and down the street to the right there will be four enemies standing there. One of them as a grenade on his belt. Shooting it will make it explode, killing all four enemies. You can then reload the checkpoint and repeat as necessary. If you haven’t unlocked it yet, using this method will also unlock Cooking Off (10G) as the distance is roughly 110 meters.
Note: Destroying vehicles with enemies in them does not count towards this achievement.
To see how many you have done, from the main menu, navigate to Extras then Career Stats. Press to highlight 'Single Player' then look for 'Explosive Kills'.
Thanks to 360GameTV for the video: