Ballista assault

creates a sphere of  rotating spectral swords 2 feet from the user facing the target chosen, which then explodes  outward as if launched from a siege weapon.

no hit dc. (don't know how to get rid of that)

low damage 3rd level initial spell with a 5th, 6th, & 7th level (or whatever's appropriate) upgrades unlocked at player level 15, 18 & 20 respectively.

once at max level, the die doubles to reflect mastery.

(initial 3 d4 for every 30 swords conjured, 1 for every ten.)

turns to 6d4 at level 15, 12d4 at lvl 18 & 24d4 at max level