DraQ
Arcane
That's pretty retarded. Even slugs aren't generally build to pierce armor, although they might work just about ok against light body armor (might not, though).99% of them suffer with pixel hunting and ridicilous difficulty level.
dafuq
True story. Not even AP ammo deal with militia than single, well placed slug.
Overall it should be:
shit tier - pistol ammo, buckshot.
bad tier - heavy pistol ammo, slugs
meh tier - ordinary AR ammo
good tier - AP AR ammo, 9x39
awesome tier - sniper ammo, AP 9x39
god tier - gauss, direct hit with RPG7.
It's pretty much how it works, or seems to in vanilla.