[Autumn]

Restricting it to "Only happens to a max of 3 times per unique attack instance" is so specific towards guns, its like you're balancing the weapon around multi-shot guns and trying to make it viable on them only, why not just power up the enchantment and have it occur only once per attack so that it can be useful to non-gun weapons too.

Powering up the enchantment to be based on Fire ATK is probably a good way to go, something like "Deals 50% Fire ATK + WPN Power physical damage on a 50% chance on crit" is probably more than enough, and really hits home some feeling of being some sort of fiery warrior I imagine.

You could also give the weapon specific perks to melee weapons as well as some sort of bonus.