Damaging with on-perk weapons and then finishing it off with an off-perk weapon divides the XP and grants it to both perks.Killing with weapons other than your current perk grants the XP to the perk that weapons belongs to.

The base damage value further modified by the difficulty-specific multipliers. Scrakes have their base health value scaled accordingly to the number of players in the game. For kill reward calculations read Dosh Mechanics.