The game has a dynamic difficulty that changes based on your actions;
You'll do less damage and take more damage from enemies!
It is based on a score system. and starts at 5,500 score / rank5
5,000 ~ 5,999 = Rank 5
6,000 ~ 6,999 = Rank 6
7,000 ~ 7,999 = Rank 7 and so on.
Dying is -1,000, getting bitten is ~-300, etc.
Shooting enemies, killing them, completing objectives, etc;
Increases your score and the game gets more difficult once you hit the next rank.
Standard caps the score at 8,999 and thus has a max rank of 8
Hardcore is always Ranks 8-9 and you start with 10,000 score.
Hardcore Score will max at 12,999 but still be rank 9.
Weapon Damage multiplier
Rank 5: x1.0 (base starting rank for standard)
Rank 6: x0.9
Rank 7: x0.8
Rank 8: x0.7
Rank 9: x0.65