In this video guide I will show you how you can easily get a kill with the turret drone explosion. Now first thing, is your going to need to upgrade it all the way for this to work. You need to find schematics to do so. The first one i got was from the wandering trader. And almost all the towns where you go to stores they have one as well. Check video to see exactly where.
Once it is level 5 you can now pick a spot to try and get the kill. Preferably that if you saved any weaker take over bases. Go to one of those and once you deploy the drone near someone your going to want to shoot it. Try to see if you can get a group of enemies together. Remember if you want to get a good group go to the mutants lairs and they will all surround you. Once you shoot the drone pay attention to see if the kill maker popped up. If not try again. It may take several attempts just so you can weaken them to the point of low health. The drone explosion is not that powerful. Once you get the kill marker the achievement will pop. It may be a bit laggy so be prepared for that.