Im having the same problem with my revalator it isnt doing any damage whatsoever even though the animation of hitting them goes through. Just tested explosive rounds on my scout and it shredded. Seems like a glitch with exp rounds on hand cannons to me

that is because the explosive damage is taken from the regular amount a shot would deal, not a crit shot. so it doesn't get a crit buff. no extra damage. so you lose out on crit shots with explosive rounds, and end up doing less damage because of it.