system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:Why are most/all sniper rifles bolt action? Why can't they use a semi-automatic mechanism like most other weapons?
gpt
I could be wrong on this, but the bolt action rifle would minimize extraneous movement that might alter the trajectory of the bullet.  Remember that even small fractions of a degree might be the difference between a hit and a miss, so it's important to keep everything as still as possible.  In a semi-automatic mechanism, the movement of the gun as it works to reload a bullet may very well knock your shot off far enough that it would cause a problem.   Nothing moves in a bolt action mechanism until you're reloading.

Edit: the bullet has a trajectory, not the gun. Edited for the proper noun.