The spell Tiny Servant (XGtE, p. 168) lets the caster create a Tiny creature out of an object:
You touch one Tiny, nonmagical object that isn’t attached to another object or a surface and isn’t being carried by another creature. The target animates and sprouts little arms and legs, becoming a creature under your control until the spell ends or the creature drops to 0 hit points. See the stat block for its statistics.
If a wizard casts Tiny Servant on a crossbow, would the crossbow be able to fire itself at an enemy?
In the statblock, the only action the servant can take is "Slam":
Slam. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 5 (1d4 + 3) bludgeoning damage.
A crossbow does 1d6 (hand crossbow), 1d8 (light crossbow), or 1d10 (heavy crossbow) damage, which is noticeably more than the Slam action. Moreover, the extra range of the crossbow would let the Tiny Servant stay out of harm's way during combat.
Would it be appropriate to let the Tiny Servant crossbow fire itself during combat?
Presumably, the Tiny Servant wouldn't be proficient in firing its own ammo, but the extra range and damage would be invaluable.