What does 50c/25 stand for? And how come second shot does so much, did you use legendary for +damage after sneak attack and tenderizer and maybe something else? Maybe any aid/food items?
50% VATS critical damage, -25% VATS AP cost tenderizer + follow through usually stacks with sneak attacks that results in high damage. 1st shot triggers the tenderizer and follow through, (legendary perk card). 2nd shot stacks with all the crit damage bonuses with tenderizer and follow through that negates resistances and damage mitigations. That's why 1st shot is not that strong, but the following shots deal a lot of damage after the perks are triggered by the 1st shot.