With Timed Payload you get an increase in damage but it gets split into bullet and explosion with the latter making most of the damage but never counting as a crit. You found a roll with incredible anti-synergy in the perks - Imo this is an insta-delete (I would rather have an empty column 3 in this case). Sidenote: Explosive payload does not share this issue. While the number from the explosion will be white, it will still count as a headshot kill. (I am aware that EP is not on this weapon. This is just for future reference)