What counts as a magically propelled attack for the 2019 UA Artificer's Arcane Armament feature?

Question

The (May 2019 Unearthed Arcana) Artificer class gets a feature that works very much like the Extra Attack feature from several existing classes, but with some additional limitations (emphasis added):

Arcane Armament

Starting at 5th level, you can attack twice, rather than once, whenever you take the Attack action on your turn, but one of the attacks must be made with a magic weapon, the magic of which you use to propel the attack.

The requirement to attack with a magic weapon is clear enough, but the final clause highlighted in bold is less clear. Presumably most attacks with magic melee/thrown weapons would not qualify as "magically propelled", but what about magic ranged weapons, like bows and crossbows? Are they propelling their arrows/bolts using magic and therefore eligible for use Arcane Armament? What if the magic weapon doesn't grant a bonus to the attack/damage rolls, but rather has some other effect (e.g. a mundane bow with Arcane Weapon cast on it)? If these would all be eligible for Arcane Armament, is there any ranged magic weapon that wouldn't be eligible?

In essence, what determines or not whether a particular magic weapon uses its magic to propel the attack? Is it just any ranged, non-thrown, magic weapon, or something more complex?

Answer 1

You can use any magic weapon with no restrictions

Starting at 5th level, you can attack twice, rather than once, whenever you take the Attack action on your turn, but one of the attacks must be made with a magic weapon, the magic of which you use to propel the attack.

First, let's start with the definition of propel:

drive, push, or cause to move in a particular direction, typically forward

Nothing about this word has any implications for the way the attack mechanically works. You can propel a sword forward with the muscles in your arms, or you can propel a thrown axe the same way. String propels an arrow attack. Or, magic can be used to help propel them as is the case here. All this bit of text was (as far as I can tell) put there to do was to draw some sort of reason why a magic weapon might result in an additional attack.

The bottom line is that the "propel" line has no mechanical impact.

If they wanted to restrict attacks to certain types of weapons they always explicitly call that out. Never have we been left to logic out what kind of weapon restrictions an ability has in any other ability and it's also not the case here.

The only restriction here is that the weapon just be magical. If it is magical and a weapon then you are all set.

Answer 2

Propel may have been a poor choice of words. The sentence fragment may have been better constructed as:

but one of the attacks must be made with a magic weapon, since you draw upon the magic stored in the weapon to make this additional attack.

This is the way that I read the statement, though I can only make an educated guess as I have no more insight into the designer's intent than you do. But a plain English reading of the sentence seems to indicate that the attack doesn't need to be made by a weapon that is normally magically propelled, but rather that the additional attack granted is granted as a result of using the magic in the weapon to fuel it.

Answer 3

Consider the scenario of a +1 enchanted crossbow, and whacking an enemy with it. Not shooting a bolt at it, but just taking the crossbow and swinging it at the enemy.

This would count as an improvised weapon attack and would not be magical, as discussed e.g. here. The magic of the crossbow is that it is good at shooting things, not that it makes a good club.

All this constraint is saying is that you can't do that. The magic weapon must be used in the way that you benefit from its magic effects, and can't be used as an improvised weapon.