Detonators from line in the sand do about 25% max health in damage. I have found this to be true when those thermals are blown with scrap bomb as well. As far a crit chance goes I am not certain which crit chance is used to calculate crit chance. They seldom ever seem to crit with scrap bomb, my scavenger had a physical crit of 52% and special crit of 37% so I would expect to see them crit more often than I do.
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