All right here me out. Here comes a terrible idea, but guns could have a set damage.
You are maybe thinking “but how do you increase the damage of a gun? and why do you have such a terrible idea”
you could replaces the gun with a better gun or infuse magic with it to make harder bullets or make them faster.
Guy works out at the gym for 7 weeks to find out that his gun does not do more damage
(If you find this a bad idea or offensive to your loadout. consider it a joke)