How does vital strike work with magus spellstrike?

Question

The magus class allows them to do two very special things, add weapon damage to spells that normally would not benefit, and have higher crit ranges.

However it occurs to me that it might also allow something else, something possibly quite powerful, and that is the inclusion of vital strike on spell damage.

Vital Strike

When you use the attack action, you can make one attack at your highest base attack bonus that deals additional damage. Roll the weapon’s damage dice for the attack twice and add the results together before adding bonuses from Strength, weapon abilities (such as flaming), precision-based damage, and other damage bonuses. These extra weapon damage dice are not multiplied on a critical hit, but are added to the total.

Now when it talks about the effect, it always mentions the weapons damage dice.

Magus Spellstrike

At 2nd level, whenever a magus casts a spell with a range of “touch” from the magus spell list, he can deliver the spell through any weapon he is wielding as part of a melee attack. Instead of the free melee touch attack normally allowed to deliver the spell, a magus can make one free melee attack with his weapon (at his highest base attack bonus) as part of casting this spell. If successful, this melee attack deals its normal damage as well as the effects of the spell. If the magus makes this attack in concert with spell combat, this melee attack takes all the penalties accrued by spell combat melee attacks. This attack uses the weapon’s critical range (20, 19–20, or 18–20 and modified by the keen weapon property or similar effects), but the spell effect only deals ×2 damage on a successful critical hit, while the weapon damage uses its own critical modifier.

So lets take the common build of a magus with a rapier and shocking grasp. The caster level will be higher than 5 so the spell damage will be 5d6 due to the BAB requirements of vital strike being 6+. So lets assume that the spell was cast on the last round so we can ignore spell combat and action economy and focus solely on vital strike and spellstrike. So assuming the attack is successful (and not a critical hit, since that critical damage does not actually matter in this case), the rapier damage is 2d6, but what about the extra spell damage? Does the spell damage get considered as part of the base weapon damage and becomes 10d6, or is it considered extra damage like the flaming weapon property and strength and not increased remaining at 5d6?

Answer 1

To understand how these interact, you must understand how these abilities work.

Vital Strike

Vital Strike is a feat that allows you to double the weapon's base damage dice when performing an attack action (standard action).

Spellstrike

Spellstrike is an ability that allows you to add a spell effect to a weapon attack through two methods:

1. While holding the charge of a touch spell, you can deliver the spell on your next successful weapon attack.
2. Instead of performing the melee touch attack you can normally do as a free action immediately after casting a touch spell (see the text below from the combat rules), you can perform a melee weapon attack in order to deliver the spell.

Touch Spells in Combat: Many spells have a range of touch. To use these spells, you cast the spell and then touch the subject. In the same round that you cast the spell, you may also touch (or attempt to touch) as a free action. You may take your move before casting the spell, after touching the target, or between casting the spell and touching the target. You can automatically touch one friend or use the spell on yourself, but to touch an opponent, you must succeed on an attack roll.

Note that spellstrike is not an action itself. It's a special ability that triggers when (#1) you perform a weapon attack while holding a charge or (#2) cast a touch spell.

How do they interact?

1. Vital Strike does NOT affect spell damage. The feat explicitly only affects the weapon's base damage dice and does not interact bonus damage from any other special ability.

2. You can use Vital Strike with spellstrike method #1. While holding the charge of a touch spell, you can perform an attack action and apply both Vital Strike and the spell effect on the attack.

3. You CANNOT use Vital Strike with spellstrike method #2. The attack action always requires a standard action, and you cannot substitute the free melee touch attack from casting a touch spell with an attack action. This means you will not be able to cast a standard action spell and Vital Strike on the same turn.

Answer 2

The spell damage is not weapon damage, so it is not rolled twice.

Roll the weapon’s damage dice for the attack twice and add the results together before adding bonuses from Strength, weapon abilities (such as flaming), precision-based damage, and other damage bonuses.

The spell damage dice (if any) would be part of the 'other damage bonuses', and so not rolled twice. Weapon damage dice are just what the PHB says in the Weapons table.

Bonus answer: You can't use Vital Strike with Spellstrike, at least not this way.

Vital Strike reads "when you use the attack action". The Attack action is a well-defined action that is a standard action. Spellstrike allows you to "deliver the spell through any weapon [you are] wielding as part of a melee attack. Instead of the free melee touch attack normally allowed to deliver the spell, a magus can make one free melee attack with his weapon (at his highest base attack bonus) as part of casting this spell." It allows you to make a single melee attack, but does not let you take the Attack Action. This is identical to normal touch-casting, where the spell lets you make a single touch attack but doesn't give you an Attack action.

You can however cast the spell, hold the charge until your next turn, and then make an Attack (or Full Attack) action, and deliver the spell this way.

Check out this FAQ for some more information how how Spellstrike works, and a user has put together a very nice explanation of touch spells, spellstrike, and spell combat here.