I am playing an Artillerist Artificer, using an Arcane Firearm (5th level feature) which states:
When you cast an artificer spell through the firearm, roll a d8, and you gain a bonus to one of the spell’s damage rolls equal to the number rolled.
Wall of fire (4th level Artillerist spell) states:
One side of the wall, selected by you when you cast this spell, deals 5d8 fire damage to each creature that ends its turn within 10 feet of that side or inside the wall. A creature takes the same damage when it enters the wall for the first time on a turn or ends its turn there.
As it's saying that the creature takes the same damage does that mean you use your first 5d8 roll throughout the duration of the spell (thus having the arcane firearms extra d8 active for the whole duration?) or do you roll each time (thus only getting the first damage boost?)