We have recently noticed, that killing a friendly hmack increases streak. Good way to make a big streak for cheaters, however kill count is not incremented. Dunno if it is known bug, but I just wanted to report it.
As far as i have seen (and tried it) shooting to friendly hmack kills u either and u have only streak one , ex. if u shoot another hmack and u have streak 3 (for example) and if u kill that friendly hmack your streak is deleted and u have streak 1