The problem I have with firearms in d20 is they don’t scale damage at the same rate as melee weapons. Firearms vary from 2d4 to 2d12. However, if we look at a bow, it will do a 1d8+STR bonus damage. So, a character with a STR Bonus of +4 will do 8.5 points of damage on average per hit. This is just shy of the average damage a 2d8 AK-47, but with a higher minimum. Crossbows allow a low strength person to fire a projectile at a higher effective strength. A heavy crossbow should do at least 1d10+4 points of damage. A firearm extends this even further. IMO, firearms should have an additive damage modifier in addition to or instead of bonus dice. In all d20 system games there becomes a point in which a melee character does significantly more damage per round than a ranged character.
For example, at 5th level a Strong Hero with a Two-Handed sword (2d6, 19-20 x2) and Power Attack, without Weapon Focus, Weapon Specialization, or a STR bonus will do 10.29 points of damage per round on average against AC 10 (assuming he power attacks equal to his BAB). That same character with a Desert Eagle (2d8, 20x2) firing at an AC 10 target at 40 feet, without Weapon Focus, Weapon Specialization, or a DEX bonus to hit will do 2.84 points of damage per round.
It just get worse when iterative attacks, STR bonus, Weapon Focus, Weapon Specialization (Soldier class), etc. However, if the target is unarmored and is hit in the chest with either a two-handed sword or a .50AE round the effect is the same.
So, in a nutshell my problem with ranged weapons is that they don’t scale damage at the same rate as melee weapons. If your character is close enough to charge his target, then why would he even bother with a ranged weapon?