Metallic Cartridges/shotgun shells transitioned from muzzle loaders to cartridges during the US Civil War (1861-1865).
Magnum simply means a more powerful cartridge. Some shotguns fire magnum cartridges. You need to define the "Magnum" you are trying to compare with a shotgun.
He didnt invent the shotgun, however he invented many different models of shotguns. auto5man
The first recorded use of the word shotgun was in Kentucky in 1776, however fire arms that functioned as what we now call shotguns predate that by centuries, having been used before the cast bullet was invented.
Just guessing- New England Firearms shotgun? If so, the answer is no. There ARE NEF rifles that can be fitted with a shotgun barrel, but not the other way. The frames for the shotguns will not withstand the higher pressures from a rifle cartridge.
cartridge
Your question, as it is asked, makes no sense. The 9mm cartridge wasn't invented until the mid 1890's.
To make it easier to hunt birds and small game. Shotguns shoot multiple projectiles that make it easier to hit a moving target.
draw for shotguns
Shotgun shells
The AA-12 shotgun( Auto Assualt twelve) and the Mosberg shotgun.
No. The M14 rifle fires the 7.62 NATO rifle cartridge. It is not a shotgun.
You need a gunsmith.