I have a Boom tool as well. It was actually at my behest that he began doing the angle cuts in them and I had him make mine 8" so it could handle a Churchill. The reason for the cut is that if you don't remove material, the hole just collapses and plugs again due to the heat and moisture. You also need to make sure that whatever you get is made of food-grade stainless. Otherwise you could get a metallic taste.