Here is the full list of all 21 Western 1849 Reloaded achievements.
Complete very hard difficulty
Kill 2000 Bandits
Kill 25 bandits in Rage Mode
Fire 5000 bullets
Perform 500 perfect reloads
Knock down 250 hats from bandits
Shoot 50 canns
Kill 100 bandits using dynamite
Complete hard difficulty
Perform 500 head shots
Perform 50 Perfect Reloads in one game
Have 2 items equipped in the backpack
Perform a 15 kill streak
Complete 3 waves in a row without losing any health
Upgrade your equipment 3 times
Complete medium difficulty
Fire 100 bullets in one game
Perform 50 headshots in one game
Complete easy difficulty
Kill 6 bandits with one clip
Complete insane difficulty