Amputations can occur when a wound deals 33% of the target’s maximum health.
If the weapon has the perk "amputates on wounds", only 22% is required, and when a wound is inflicted it is guaranteed to cause an amputation (light wounds do not count).
Amputation of vital limbs immediately kills the enemy, unless the limb is robotic.

I drafted a table of minimum base damage for amputations with weapons that has a perk, taking into account the barons’ armor (and the resistance it provides)

And a table for main gold mine in the game

table[docs.google.com] for future use, in case anyone wants to calculate something else