Just to add some variety for handgun challenges, we could add a new type of ammo and handgun, and perhaps change the existing handguns just a wee bit to make each interesting and unique.
For revolvers, we could use perhaps .357 mag or .44 mag, give them a 5 or 6 round capacity, higher damage, slower reload.
For semi-autos using 10mm, bump up the capacity to around 12 perhaps. Lower damage and faster reload than revolvers. Maybe a touch higher accuracy.
This type of change could be applied to existing uniques and whatnot such as Trigun, which is a revolver.
It'd make AoMr a little more interesting than grabbing just 10mm, and with the two types that could be balanced against each other, it might offer some interesting play experiences.