Well I'm no gunsmith and I was actually looking for the same answer. I went ahead and loaded 3" magnum shells in my 1100 Lt 20 GA chambered for 2 3/4 shells and fired and it shot just fine and cycled just fine. Although my 1100 is very picky about what it will cycle like any low brass shells, it WILL not cycle (and that may just be this particular gun) but the 3" went through just fine like I said there for in my opinion (for what it's worth) they seem to do good with the 3" mag. Hope this helps and if there is no objection from anyone who knows better than I do give it a try and see what happens.
The sizes of shells it accepts will be stamped on the barrel
NO!!
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.
No
If has the magnum cylinder it will.
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.
Check related links to Remington Society of America for barrel date code information.
sure - clean it afterward
I have a model 1100 Lt 20 ga. magnum and it will fire the 2&3/4 shells but will not cycle or eject them. Someone told me that the holes in the barrel to let the gas escape are different on the magnum. I bought another barrel for 2&3/4 shells and it cycles them fine with this barrel.