I've noticed quite a few threads about decapitations, usually about the crossbow, stating that the numbers do not match up. This is incorrect. What some people are omitting is that head shot decapitation instant kills only require that the attack does
A) 15% of the specimen's current HP
B) brings the specimen's total remaining HP to under 50%
Example:
Scrake (1000HP + 500HP per player) * 1.35 HARD / * 1.75 SUICIDAL
Scrake 6 Player Suicidal - 6125 HP
Damage required to instant kill at 100%: 3062.5
A) 918.75
B) 3062.5
Damage required to kill at 50%: 1531.25
As the Scrake takes damage, it becomes easier to decapitate with less powerful attacks. This is the reason Perks without bonuses to the crossbow are able to kill Scrakes in 1-x bolts.
A) 15% of the specimen's current HP
B) brings the specimen's total remaining HP to under 50%
Example:
Scrake (1000HP + 500HP per player) * 1.35 HARD / * 1.75 SUICIDAL
Scrake 6 Player Suicidal - 6125 HP
Damage required to instant kill at 100%: 3062.5
A) 918.75
B) 3062.5
Damage required to kill at 50%: 1531.25
As the Scrake takes damage, it becomes easier to decapitate with less powerful attacks. This is the reason Perks without bonuses to the crossbow are able to kill Scrakes in 1-x bolts.