I am a complete rookie when it comes to BH209. Shot it for the first time this past weekend. Based on what I've learned from here and MM, I would say that improper bp design and/or a restricted flame channel would cause the most problems.
I do know that I had a flawless maiden voyage (albeit only 12 shots), so I am happy. Still have alot to learn with it but it shot good and was nice to not have to swab between shots.