Why do shotgun shells have brass or steel encasing the base while

Why do shotgun shells have brass or steel encasing the base while the rest of the shell is composed of paper or plastic? Is it necessary? - Quora

I got my grandpa Winchester model 25 12 gauge pump action shotgun and I'm trying to figure out if it should be able to fire steel birdshot or do I need to

What is thicker, 12 or 14 gauge steel? - Quora

Cartridge, Types, Calibers, Ballistics

Minié ball, bullet

Cleaning 10 Gauge Brass Shotgun Shells Presented by Larry Potterfield

I've seen short gunshot shells or mini shells for the first time last week. I'm a reloader and I reload shotgun shells. Seems like I can crank out a bunch of these;

Why are shotgun shells all rimmed? - Quora

Constantine Holy Shotgun Cartridge Replica