system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do automatic guns deal with the heat that would be created from the friction of so many bullets passing through the barrel so quickly?
gpt
Some automatic guns, typically machine guns, have replaceable barrels that are meant to be interchanged when they overheat. Some older machine guns were even water-cooled, or had rotating barrels that would share the thermal load (i.e. the classic Gatling gun).

Otherwise, the barrels are just kept well ventilated so that airflow will cool them off. Most automatic weapons, like assault rifles, aren't really meant to be fired continuously, so overheating isn't much of a problem in normal use.