Bottomline: If you're going to be using different brands of paint, the bore sizes are going to differ. I realized this after years of trying to find different barrels for my marker to fit all brands of paint, and I broke down and bought an Evil Pipe barrel system. Best investment I've ever made, and it cost me hundreds less than buying different barrels with all those different bore sizes would have. If you are going to go with 2 Boomies though, I'd say .686 and .690. That should keep you pretty well set for medium/small and medium/large bore paint