I'm working on a few variations to try to clean this up. The one I'm thinking of most strongly right now is level 1 letting you make a ranged attack with an ammo weapon when you cast a cantrip. This will let you deny saves and use the weapon to hit to hit a single target, and use the weapon's range for the cantrip. If an AoE, its origin is where the ammo hits. Some language included to allow aiming at a point in space for AoEs. It will take some cleaning up. But if you think of it as letting a single target get no save on save-allowing cantrips, extending the range, and still hitting other targets normally (with the ammo as "focus" for anything determining where the targets are relative to each other), that captures the idea.

Then, at level 6, give them the ability to cast a spell that uses roughly the same rules whenever they make an attack with an ammo weapon. This will have language preventing it from stacking with the level 1 feature (no cantrip->attack->spell), and preventing it from itneracting with a multishot trick shot (that'll count as a single attack, and enable multiple targets for things like eldritch blast or scorching ray or magic missile). Level 6 still gives access to trick shots.

This probably doesn't do much on its own, but if you're using hand crossbows, you could TWF to fire off two spells. Though that does bumble around the existing rules about casting spells as bonus actions, which may need thought and addressing.

Level 14 gives them the extra attack.

A pure Sorcerer of this subclass would thus get two spells off in a round - maybe 3 if they really pushed it with TWF - at level 14. A multiclasser would have the level 6 feature and their level 5 extra attack from another class at level 11, which...I think I'm comfortable with. But it may be overpowered, still.