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

When was the 12 gauge shotgun shell invented? - Quora

What were shotgun cartridges made of before plastic existed? - Quora

A Brief History Of Ammo - Wideners Shooting, Hunting & Gun Blog

Winchester No. 12 Brass Shotgun Shells Circa 1890

How can a shotgun shell with a powerful charge use a plastic case, but rifle shells have to be metal? - Quora

Base Wad Separation

Why are shotgun shells made of plastic? - Quora

If shotgun shells are made of plastic, is there a risk that they might melt inside the magazine tube after prolonged shooting? Or is this not an issue with most modern shotguns?

Full Metal Jacket Bullet - Interesting Things To Know

How Do Shotgun Shells Work? What Are Shotgun Shells Filled With?

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

Full Metal Jacket Boat Tail Ammo at : FMJ-BT Explained

How do shotgun shells work? - Quora