Alla-kaBLAM

You touch one round of firearm ammunition and whisper an incantation to turn it into a round of kaBLAM ammunition. If fired at a creature with a ranged firearms attack, on a hit this ammunition latches into the creatures body and requires the creature to use an action to make a medicine check against your spell save DC to remove the round, at which point it becomes inert and the spell ends. At any time that a round is still active within a creature you may use your reaction to say the trigger word AllakaBLAM and any active rounds from your spell will explode in a 10ft radius cloud of fire centred on the round ending the spell. Any creatures within the area of effect must make a DEX save against your spell save DC or take 3d8 fire damage on a fail or half as much on a success.

At Higher Levels. When you cast this spell using a spell slot of 3rd level or higher, you create one extra kaBLAM round for each slot level above 2nd. Note that using your reaction to say kaBLAM makes all currently active rounds explode at once and all other rounds become inactive and the spell ends.