Here is the full list of all 48 Necromunda: Hired Gun achievements.
Finish the Main Campaign
Travel 5km using the grapnel
Finish Chapter 12
Finish Chapter 11
Finish Chapter 10
Finish Chapter 9
Finish Chapter 8
Finish Chapter 7
Take out 50 shields with the grapnel
Upgrade one implant to the class 4
Finish Chapter 6
Open 20 chests
Kill 30 enemies with the Crush module
Find a +3 weapon
Finish Chapter 5
Finish Chapter 4
Amass 100.000 credits
Buy an upgrade for your Mastiff
Kill 10 enemies in a row with headshots only
Kill 30 enemies with your Mastiff
Finish your first secondary mission
Finish Chapter 3
You have killed 100 enemies with a headshot
Finish Chapter 2
Let Brickjaw live in Koloss 44
Pet your dog in Martyr's end
Buy your first upgrade to the Rogue Doc
Finish Chapter 1
You have performed 100 Takedowns
Fill one faction bar
Wallrun 2500m
Finish a mission with an S rank
Kill 100 enemies while wallrunning
Kill an enemy with every weapon
Kill 100 enemies by using Augmetics powers
Finish all main missions with a rank of A or more
Complete the shooting training in Martyr's End
Customize every aspect of a single weapon
Finish Kaerus without using any other weapons than the Ironfist
Finish Avarus without using the grapnel
Place the 5 bombs in a gap of less than 3 minutes in Escher Lab
Kill a Genestealer with a grenade launcher
Finish a mission using only special weapons
Kill 5 enemies in one use of Strength Booster
Kill Brickjaw in Koloss 44
Kill 30 enemies with the Blast module
Kill 60 enemies with the Perfect Aim module
Trigger all mines on Steel way