Here is the full list of all 37 Ballistic Overkill achievements.
Try to open a door
Killed by lava
Kill 500 enemies with SMGs
Kill 500 enemies with Machine Pistols
Kill 500 enemies with Sniper Rifles
Kill 500 enemies with Shotguns
Kill 500 enemies with Assault Rifles
Kill 100 enemies with Grenades or Grenade Launchers
Unlock your first accessory
Killed by falling into one of Citadel’s holes
Kill 2 enemies with the same grenade
Get an Overkill
Kill 100 enemies with Melee Attacks
Kill an enemy while inside of Hollow’s tube
Get 20 savior kills
Finish a match with more than 1500 score
Kill 5 enemies while in the King of the Hill point in the same life
Kill 3 enemies with the same weapon without reloading
Deal 2000 damage in a single life
Kill 2 enemies with backstabs within 5 seconds
Capture 3 points in the same life in Capture Point mode
Get 30 kill assists
Drop your first Lockbox
Kill 500 enemies with Pistols
Kill 1000 enemies with headshots
Play a thousand matches
Kill yourself with a grenade launcher right after jumping
Kill yourself by jumping from a very high place
Killed by being smashed by one of Overhead’s cranes
See a ghost in Blackfield
Look at every painting in Nox Museum in a single match
Break all glasses in Sunsquare Mall in a single match
Look at an out-of-the-way piece of advertising in Wonderdome
Find a place to play F2P Ballistic
Write and send on chat all words in Hakim’s Hunting Words board in a single match
Shoot all the coffee machines on Corporate Park in a single match
Kill 500 enemies with LMG