system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:Why is it that the barrel of the gun is the part that becomes hot when fired instead of the area where the bullet is struck from?
gpt
1.  The brass shell casing absorbs quite a bit of heat which is then carried with it when it's ejected after each bullet fires.

2.  The area around the chamber tends to have a good deal more metal in it than the barrel, so it takes more energy to heat it up.

3.  The chamber does get quite hot during prolonged firing. Machine guns fire from an open bolt in large part so that you're not putting a live round into a firing chamber that's so hot that it will just go off spontaneously.