use it as your primary weapon. just switch to that every time you spawn and use it up before you go to your regular weapon. this will increase your chances. play only hardcore DOM.
i got mine on grind comming from A to B at the start of a match. RPG into the window above the ramp behind B and got 3 people rushing to B.
You have 2 rockets in that thing. Fire one then duck into covert and then fpop out and fire another one
crossbow challenges are easy in sticks and stones (except thirsties). you can get your ballistic knife stuff there too.
i got my rpg on plaza domination on b flag. was running up the steps and aimed it up at the ceiling/overhang above the flag. all suggestions above are winners tho.