The ‘Artillery Shot’ ability unlocked by French Royal Cannons states that it does an extra 30% damage. However, it seems to just deal a flat 899 damage.
- Before the most recent patch, they should have been doing (72 + 650) * 1.3 = 938.6 damage
- After the most recent patch, they should be doing (72 + 585) * 1.3 = 854.1 damage
But in both cases, the attack deals 899 damage.