As far as damage goes, I would recommend looking at Spycraft instead of d20 modern. Example is looking at a Beretta M92FS (an M9 as most know it) and an M1911A1. D20 Modern M9 damage 2d6, range 40ft, Crit 20 M1911A1 damage 2d6, range 30ft, Crit 20 Spycraft M9 damage 1d10+1, range 20ft, Crit 20, error 1-2 M1911A1 damage 1d12, Crit 19-20, error 0 Spycraft allows for a bit more variability in it’s weaponry while keeping them from getting ridiculously overpowered. It provides for a difference on the damage based on caliber without going into the deep end. And it provides an easy example for the P90. But that depends on how armor is handled in this system to determine how it would be defeated or penetrated.