Running with just the Xenos mods and AAI, the bots don't seem to be doing damage with bullets. I'm putting them against starting biters and they do 0 damage or so I am seeing.

What ammo are you using?
What ammo-changing mod do you have?

For exemple, K2 does affect ammo (all of it?)

Will investigate on my side when i'll have a moment

I'm using vanilla ammo and only AAI mods and your mods. No mods that should change ammo.
Trying with vanilla ammo and uranium ammo. Explosive ammo seems to work fine.

Guns are showing negative bonus damage
EDIT: Ignore this note. that should effect base damage. Not actual damage.
But actual damage is 0. 15 HP starter biters are taking no damage from them.
I can kill them myself and AAI chain guner can kill them just fine.
EDIT2: More testing. Looks like a range thing? When they get into melee range the bullet damage is applied and poof they die.

Oh, i get it.
There's a minor change required for it to work with vanilla.

My bad.

Will be able to fix that later.

Until fixed, you may use ammo from this mod: (else mods might also work)
https://mods.factorio.com/mod/alr-ac ammo

P.S.: yes, the -xx% damage is normal. It is a damage reduction

Looks like that suggested mod ammo isn't quite working either

I removed lead_target_for_projectile_speed from the bot guns and suddenly they work fine.

You see, you don't make things worse!

Did some short tests on vanilla - everything worked fine... lead_target was on

Disabled the lead_target - just in case- temporarily.

Re-uploaded x)

EDIT: Haven't updated to new version yet.
So removing lead allows vanilla instant hit ammo to work. It also seems to allow your fancy HE ammo to work but it no longer leads the target. But hits do damage (and wreck the biters) So how do you make it lead the target with projectile ammo and not lead with instant hit ammo?

Will switch the assault(+precision) rifle robot to he/stun he with lead on.
The rest will stay with vanilla ammo and lead off.

Or a lead_on weapon version for everyone xD
(x2 robot amount tho...)

Or simply put a lead_on version of the mod up