Iron Brigade

you will need the U0-FM "Fighting Wolverine" sniper riffle for this. i tried alot using other lower powered snipers with ricochet and it was almost impossible. you need the extra damage plus ricochet+ for this to work.

its a purple sniper that you will get near the end of the game. it has the Ricochet+ ability, and once you have it, just fire it at huge piles of enemies and you will get it eventually as the shots bounce off each other.

Refinery is a good map to try it on since it has narrow corridors that shots can bounce off, if you want to farm it. But it really doesnt matter since i ended up getting it randomly on Volcano. It has a lot of luck involved so you might get it on your first try or your 6th/7th.

Trickshooter
Kill an enemy with a ricochet sniper shot after 4 bounces

Equip the U0-FM "Fighting Wolverine" sniper rifle. You will need to be level 10 to equip this weapon.

Load Africa/Sinkhole.
I picked this map because there are a lot of Resistors and they gather around the bomb making them easy targets. I got it on the 3rd wave on my first attempt.

Go to outer edge looking down toward the bomb. I stood up near the "v" shaped wall. Take out the first 2 waves any way you prefer. Who knows, you might get lucky. Your first best opportunity will be on the 3rd wave. You will get 8 Resistors that will go directly to the bomb. Let them gather there then shoot the ground near them. If you don't get it, protect the bomb until the 7th wave and try again.

Good Luck!