Here is the full list of all 20 Rusty Gun achievements worth 1,000 gamerscore. It takes around 1-2 hours to unlock all of the achievements on Xbox One.
Completed the game
Completeв the level on boat
Killed the fourth boss
Completed the level on skateboard
Killed the third boss
Killed the second boss
Performed 50 slides
Blowed up on three mines
Died 15 times
Found a calendar
Completed the car level
Killed the first boss
Killed 150 enemies
Don't talk, just crouch till you drop. 44 times, to be exact
Jumped 200 times
Killed 72 enemies
Collected 50 bottles
Completed first level
Killed 30 enemies
Killed your first enemy