In the game I DM for, one player is playing a ranger. The player asked me if he would be able to cast the lightning arrow spell, then use the arrow as ammunition for the conjure barrage spell.
The lightning arrow spell (PHB, p. 255) has a casting time of 1 bonus action, and a duration of "Concentration, up to 1 minute":
The next time you make a ranged weapon attack during the spell’s duration, the weapon’s ammunition, or the weapon itself if it’s a thrown weapon, transforms into a bolt of lightning. Make the attack roll as normal. The target takes 4d8 lightning damage on a hit, or half as much damage on a miss, instead of the weapon’s normal damage.
Whether you hit or miss, each creature within 10 feet of the target must make a Dexterity saving throw. Each of these creatures takes 2d8 lightning damage on a failed save, or half as much damage on a successful one.
The conjure barrage spell (PHB, p. 225) has a casting time of 1 action and a duration of "Instantaneous":
You throw a nonmagical weapon or fire a piece of nonmagical ammunition into the air to create a cone of identical weapons that shoot forward and then disappear. Each creature in a 60-foot cone must succeed on a Dexterity saving throw. A creature takes 3d8 damage on a failed save, or half as much damage on a successful one. The damage type is the same as that of the weapon or ammunition used as a component.
The rule on bonus-action spellcasting (PHB, p. 202) states:
A spell cast with a bonus action is especially swift. You must use a bonus action on your turn to cast the spell, provided that you haven’t already taken a bonus action this turn. You can’t cast another spell during the same turn, except for a cantrip with a casting time of 1 action.
But then on the next page, it also states in the rules for concentration (p. 203; emphasis mine):
Normal activity, such as moving and attacking, doesn't interfere with concentration. The following factors can break concentration:
- Casting another spell that requires concentration. You lose concentration on a spell if you cast another spell that requires concentration. You can’t concentrate on two spells at once.
Would the ranger be able to cast both spells in the same turn?
I interpret the last quote as meaning that you can cast 2 spells, if 1 requires concentration and the other does not, unless a spell doesn't count as an attack.
If he can't use them in the same round, could he cast lightning arrow, save it until the next round, then use it for conjure barrage?