system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: why is it that long distance shooters tend to use bolt action rifles? Can a magazine fed semi-auto not do the same job?
gpt
A semi-automatic weapon uses either some of the recoil from a shot, or gas from the shot to cycle it's action.  This means that the action begins moving while the projectile is still inside of the weapon.  The motion of the action moves the gun, and can affect the accuracy of the shot.  

A bolt action stays in place and remains a solid unit the shooter manually works it.  This reduced amount of motion leads to greater accuracy. 

Great strides have been made in making the actions of certain semi-auto weapons more stable and accurate, and there are a lot of solid options available.  At the end of the day though, if we're talking the absolute best weapon with each type of action, in the hands of a highly skilled shooter, the bolt action will win out.