Here is the full list of all 40 Shellshock 2: Blood Trails achievements worth 1,000 gamerscore.
Completed a level firing only a pistol
Completed the game without being killed by an Infected
Completed the game twice
Killed 15 enemies with one belt of a non-mounted Heavy Machine Gun
Completed a level without dying
Killed 15 enemies with the machete
Completed the game on Easy
Completed the game on Normal
Completed the game on Hard
Completed Mission 10 on Normal
Completed Mission 10 on Hard
Completed Mission 9 on Normal
Completed Mission 9 on Hard
Beaten down 15 enemies
Completed Mission 8 on Normal
Completed Mission 8 on Hard
Killed 5 enemies with one AK47 clip
Completed Mission 7 on Normal
Completed Mission 7 on Hard
Killed 3 enemies with one rocket or grenade
Found and picked up every weapon
Completed Mission 6 on Normal
Completed Mission 6 on Hard
Completed Mission 5 on Normal
Completed Mission 5 on Hard
Completed Mission 4 on Normal
Completed Mission 4 on Hard
Dismembered 50 enemies
Scored 15 decapitating head shots
Completed Mission 3 on Normal
Completed Mission 3 on Hard
Killed 150 enemies
Completed Mission 2 on Hard
Completed Mission 2 on Normal
Killed 5 enemies with one M16 clip
Completed Mission 1 on Normal
Completed Mission 1 on Hard
Scored a decapitating head shot
Killed 3 enemies with one pistol clip
Beaten down an enemy