Here is the full list of all 13 A Fistful of Gun achievements.
Headbutt a train
Finish story mode
Score a Wild Wild combo
Survive a peyote trip
Defeat the KKKrusher
Ride the Soul Train
Shoot down a totem pole
Kill 100 gunslingers
Punch 100 bandits
Shoot a flaming bear
Shoot a flaming dog
Win the game in No Card Mode
Rob a bank