If you mean a Remington 512 X Sportsmaster, no. It is for .22 Short, Long, Long rifle cartridges. The .22 magnum is longer, larger in diameter and more powerful.
The Light will only accept and shoot 2 3/4" shells. The Magnum will shoot up to 3" 20ga shells.
If has the magnum cylinder it will.
The sizes of shells it accepts will be stamped on the barrel
In a .44 Magnum revolver, yes. In a semi-automatic .44 Magnum (such as the Desert Eagle), no.
No, they are different sizes.
In general, no. Unless the gun is marked for 3 inch (or even 3 1/2 inch) shells, you should not attempt to fire 3 inch Magnum shells, even if they seem to fit. However, if you have a gun made for 2 3/4 inch shells, and have 2 3/4 inch "magnum" shells, IF your gun is safe to shoot, it should be safe to shoot those "baby" magnums.
sure - clean it afterward
Yes, however, they may not cycle thru, and need to be loaded one at a time. Chamber will need cleaning after shooting the shorter magnum cartridge.
A .357 Magnum can shoot .38 Special rounds as well as .357 Magnum rounds.
Yes, they are all high brass and considered magnum loads
NO
When were 3inch magnum