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

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

Redneck Convent Ammo Storage Box - Tan .50 Caliber Ammunition Flip Top Lockable Storage Box - Waterproof Metal Military Ammo Can Container - Airtight Latching Dry Box Bullet Case Steel Field

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 are TMJ and BEB Bullets?

Why are shotgun shells made out of plastic while rifle shells are made of metal? - Quora

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 there no low brass, 3.5” 10 gauge shells loaded with #8 birdshot? - Quora

What is the diameter of a 12 gauge shotgun shell right before the rim? - Quora

Base Wad Separation

Why don't shotgun slugs and shot use full metal jackets and why don't other guns use plastic casings? I believe shotgun shells were originally full metal. - Quora