I've been maining Gunslinger and if I find myself against a BD-heavy team, I'll hold onto my supercharge until I hear someone activate BD. One shot kill to prevent a knifing spree and you can feel their rage... Also, I've been having some great fortune in taking them done before they get to me even without the super. Gambler's dagger + knife juggler means I'll typically have at least one knife on CD. Throw one (or both if available) of your knives at an oncoming BD and if you can manage to get off some headshot rounds they'll fall far before they get to you. In close quarters, though...