I never knew about fire ammo damage changing with weapon damage, that's cool. also this might be common knowledge but: fire ammo does a good deal of damage to tanks, and it doesn't stack, so shooting it (or any other special infected) once every 2 seconds once they stop burning is the best way maximise the total damage from a magazine of fire bullets. also, a single fire bullet can ignite more than one common infected, making it surprisingly useful for crowd control, if you have no other choice.
Oh no LOL, fake news. I have actually found another tip from the wiki though: Fire ammo damage completely ignores SI resistances, so it ignores the bullet and melee damage resistance that the orange/pink/red SI have. So that's cool!
