How much damage is done by a monk's Deflect Missiles feature when deflecting a Crossbow Bolt?

Question

Similar to this question about using Deflect Missiles against unusual projectiles, but way simpler.

The monk's Deflect Missiles feature states:

If you catch a missile in this way, you can spend 1 ki point to make a ranged attack with the weapon or piece of ammunition you just caught, as part of the same reaction. You make this attack with proficiency, regardless of your weapon proficiencies, and the missile counts as a monk weapon for the attack, which has a normal range of 20 feet and a long range of 60 feet.

Assume a Monk is hit by a Crossbow Bolt and manages to nullify the damage. The same Bolt can be used by three different Crossbows (Hand, Light or Heavy), to deal 1d6, 1d8 or 1d10.

Does the damage dealt by the reaction attack from Deflect Missiles depend on the weapon that was used to attack the Monk in the first place? That seems very weird, since the difference is pretty much only the speed that the crossbow fires the bolt - which is meaningless once the Monk has stopped the shot.

In particular, the text states that the missile counts as a monk weapon for the attack. Does it mean we should use the damage from the monk's Martial Arts feature?

You can roll a d4 in place of the normal damage of your unarmed strike or monk weapon. This die changes as you gain monk levels, as shown in the Martial Arts column of the Monk table.

The problem here is that it says you can replace the weapon damage for the Monk Dice (this is how I call the dice from the column), but not necessarily has to.

So, what damage dice do I roll if the reaction attack from Deflect Missiles hits?

Answer 1

Damage as an improvised weapon (or the monk's Martial Arts die).

Strictly speaking a crossbow bolt is not a weapon. No one has proficiency with crossbow bolts and there is no stated damage die for a crossbow bolt. If another character were to attempt to throw a crossbow bolt it would be treated as an improvised weapon.

At the DM's option, a character proficient with a weapon can use a similar object as if it were that weapon and use his or her proficiency bonus. An object that bears no resemblance to a weapon deals 1d4 damage (the DM assigns a damage type appropriate to the object).

Using this interpretation the weapon would either deal 1d4 damage, damage according to DM interpretation, or the damage of the monk's Martial Arts die.

There are reasons to think that a DM would consider the crossbow bolt as thrown by the monk to be comparable to the crossbow bolt as fired by the original crossbow:

• The crossbow bolt fired by a Heavy Crossbow is actually different from the crossbow bolt fired by a Hand Crossbow. They are treated as the same item in the book as a way of reducing complexity but they represent different types of items. This is the same type of simplification that allows armor to frequently fit a character without needing to be re-made.
• The different damages of the different crossbows represent different speeds at which the bolt is fired. The deflecting of the bolt might preserve this momentum and so thereby preserve the original damage.¹

If a DM agrees with these understandings then they might very well rule that the crossbow bolt should deal damage equal to the damage of the weapon that originally hurled it.

This also appears to be RAI considering this Jeremy Crawford Tweet that mxyzplk-SEstopbeingevil found.

^{1: This is based on an imagining about how deflecting missiles takes place. Technically the monk catches the missile and then chooses to make an attack with it. Since it all takes place as a reaction, however, I envision it as one fluid movement where the monk redirects the missile towards a new target.}