I used Subtle Calamity and Duke. Stick to cover and nail em with the bow on your engagement. If you can nail someone once with an arrow, generally they'll do one of two things, duck out or keep firing. In either case, they wont expect you to throw out another quick burst of damage from something like a hand cannon after you drew a bow, and Duke's impact can clean up after an arrow headshot. Try to find one with Rangefinder or Opening Shot to help with headshots, and put a free hand mod on it to help with ready speed if you combo it with the bow. :)