Thread: How does brass "grow"

I'd like to understand the basics behind case expansion a bit better.

Assuming you have a cartridge that headspaces off the shoulder, and you are loading fire formed cases for a single rifle.

After each firing the case is slightly longer. Does this brass "flow" from the thick part at the base (the web), so that eventually the web gets thin and you start getting failures ?

If you neck size fireformed cases, what is it that eventually causes the case to be difficult to chamber ? Is it purely neck length, or something else further down the case ? If it is neck length, you should theoretically be able to trim each time and keep neck sizing...