To hit small things, you should use VATS aiming; i.e., look at the target, quickly open and close VATS, then fire.
Saves AP, great for long-range with weapons that have low-to-zero spread.
Also guys, keep in mind, this is an RPG based on dice-rolls, not really a traditional FPS. It's not really designed to play like an FPS in a lot of respects.
For example, your minimum spread is a static value, but where your gunsights are pointing while aiming is not; thus, where the bullet ends up is a function of a few things; these are predominantly dependent upon your gun skill and strength (changed in Fallout 4 to perks + strength), as well as the weapon you are using.
As an example, sniping has historically required high strength for greater accuracy (STR > 8, or Steady Hands perk). Yet you'll see a lot of guys frustrated about sniping in Fallout, not realizing they don't really have the prerequisites to use the weapon at a high level of accuracy.
All of this in combination affects your ability to hit your target - yes, even outside of VATS.
A lot of folks can't get used to this idea, because this is not how first person shooters traditionally work. This is why Lincoln's Repeater, among a few select weapons, was the most widely used gun in FO3 - since it was an early-game, zero spread, rifle. New Vegas made this much harder, but made iron sight aiming more reliable.