'set health' kills doesn't drop items, how can i fix this?

i was trying to make a weapon that increases in attack damage, i initially used 'Deal # damage to 'event/target entity' from source #' but because it was during the I-frames of the attack i decided to look for another method.
that's how i came to the conclusion of using 'set health' to deal said extra damage, and while that has worked, when it's not killed by the weapon's base damage it doesn't drop any loot.
does anyone know a possible alternative, or how to fix the dropping issue?