d20 Future Tech gives us the beauty of the nanoround. This programmable type of ammunition inflicts no damage on a hit. Rather, it inflicts ability damage every round for 1d3+1 rounds, no save. Your options are:
Flesh: 1d4 Con damage/round
Bone:1d4 Str damage/round
Nerves:1d2 dex/1d3 int/round
and a few other versions for dissolving doors, walls, and other annoying objects.
Might I ask what they were thinking? And yes, you can change what it damages as a free action.
EDIT: And the CR is utterly fucked up. A basic gun drone, much like a Walker in Deus Ex, is 1/2 CR. It can inflict 3d8 damage per shot. It has 30 HP. The Damn thing also looks like a crab, for what I guess are obvious reasons.
