> i have the biggest trouble with the concussion rifle, i can’t get a damn kill with it. also any support as with the needler as to the best way to kill with that as well. all others i have covered, if not mastered. but that concussion!!! noooo!!! haha thanks for the help man 
the concussion rifle is a very tricky one. first thing first you’re going to want to make sure you have the ammo mod on (more shot mean more potential kills)
concussion rifle is really only good when your enemy has their back against the wall. you’ve probably noticed that if you shoot someone point blank it doesn’t do as much as it should, or at their feet they can jump and it will be as if you boost them up. but it is really good if you shoot them against a wall.
best maps for the concussion rifle would be any of the majestic maps, longbow (if you can camp the middle base inside, not ontop) or exile.
there are two loadouts,
primary - assault rifle (lowers shields quickly)
secondary - concussion (when u call it in)
armor ability - jet pack
support - ammo (the other loadout is the same but with dexterity)
if you use the loadout with ammo then they best option is to fly above your enemy and be a phantom and just rain fire onto their head (this usually got me killed more because you are more exposed)
if you use dexterity then shoot them till they are one shot with the assault rifle (it lowers there shields very quickly) then quickly switch guns and shoot 1-3 shots at their feet or at them.
its pretty annoying using this weapon, so good luck!
EDIT: and needler is really good in long hall ways, it is usually a first ordnance on a few maps. needler’s loadout can be anything, as long as it has ammo because it burns through it.
my best maps would be haven, monolith, exile, and longbow.
all of the bottom part of haven is good. the top parts are a lot harder to get a kill with, and stand by the ramps to the top, you’ll only need to worry about dmrs and brs.
exile i would go to the middle and look down the cave ramp where the enemy team comes for, or stand near it.
monolith would be anywhere near the middle, don’t go to the center of the map or outter part of it because it has a lot of cut-away points.
longbow is more difficult, but at the top of the gravity lift looking at the enemy spawns.