Eöl's Autonomous Crossbow

Throwing the crossbow bolt into the air, you shout the incantation and weave your hands in the appropriate arcane gestures, and the bolt disappears, upon which a floating heavy crossbow appears at a point of your choice within range. Once the crossbow appears, you may choose a target (a creature, object, or a point in space) that you can see within 400 ft. of it. On your consequent turns you may use your action to assign the crossbow another target which you can see within 400 ft.

On each of your turns while the spell lasts (including the turn on which the spell was cast) you may use your bonus action to instruct the crossbow to attack its designated target. As long as the target is within range of a heavy crossbow (100/400 ft.) and does not have full cover from the crossbow, the crossbow winds itself and a similar bolt to the one used to cast the spell is created and fired. The crossbow attacks using your spell attack modifier, and on a hit deals 1d10 + your spell ability modifier piercing damage which is considered magical (if the bolt had any special properties, they are taken into account for the first shot fired by the crossbow). Once the attack is resolved, the bolt disappears.

The crossbow is made of wood and steel, and has an AC of 15 with 10 hitpoints. However, since it presents a very small profile, ranged attacks against it are made at a disadvantage.

If cast at the same spot every day for three months, the spell becomes permanent, and any creature standing at the casting point can control the spell. If the same type of bolt is used at every casting, every bolt fired by the crossbow(s) is of that type, not just the first.

At Higher Levels. When you cast this spell at 3rd level or higher, one additional crossbow is created within range for every two levels beyond first. When you designate targets on any turn you may designate a different target for each crossbow. If the bolt used to cast the spell had any special properties, they are taken into account for the first shot of each crossbow.