I found the best way (from my position in the campaign so far) to get this achievement is on Rakks, (The flying bat-type enemies) The place I got my achievement was at Southern Shelf - Bay. This is located very early on in the game where you open the giant gate with the help of Sir Hammerlock. after you exit the gate if you walk forward and turn to the left some you should see the area where you are supposed to be headed,(when you get close you should notice the electric barrier blocking your path forward.) Clear out the enemies, destroy the core to move the barrier out of your way and go straight and take a left entering Southern Shelf - Bay. Take a left out of the cave when you arrive in the new area and kill some of the bullymangs there to give you some space. If you look up you will notice the Rakks i mentioned earlier. Make sure you have your Tediore weapon of choice and have at least one shot fired from it making it able to be reloaded. You should try and get on a fairly high edge to get the Rakks to notice you and attack. When you see them beginning to lunge at you press the reload button to throw your gun hopefully getting your achievement! You may have to weaken them a little as the gun explosion doesn't seem to do much damage but all in all this is a fairly simple achievement and shouldn't take long at all to get. :) also this is my first solution guide so try not to bash me too hard lol. Edit: Thanks to xblChoas for letting me add his video to my solution.