Small to medium was the right choice here. Stable enough to carry around, powerful enough to kill. In the end the easiest thing to do was go to one of the websites that does all the work for you. Custom-make the bomb to your specifications, deliver it, even help you to place the thing if that’s what you need. This particular company had received very good reviews. They even offered a money-back guarantee if the bomb failed to go off. They’re called Boom or Bust.
