For Small Guns... Vault City Patrols have sniper rifles and .223 pistols. Raiders (Khan, north of Broken Hills) have FN FALs. Unity has Assault Rifles. If you are critical build, then sniper rifle is your best bet.
Marauders, Traders, Regulators, Raiders (Khan), and some others have Grease Guns, which is a nice bursting weapon.
Accuracy is accuracy. If you 1-hex someone with 95% accuracy, which would mean less than 95% skill needed due to perception, then it will usually always hit the person with all bullets. One bullet may go astray sometimes and not hit, but you can't prevent that. (Chances are you're going to want Bonus Rate of Fire, though, which requires 180 skill. Or at least some Bonus Ranged Damage perks, see the wiki for their requirements.)
Bursts that are not 1-hex usually hit with 1/3 amount of burst, or so I think dev has said.