NO! This is EXTREMELY dangerous!
You could eaither shoot dove with a 20 gauge shotgun or a 12 gauge shotgun. You should also use a bird shot shells
Yes, shorter shells are no problem.
yes
No, you can not shoot anything but 12 gauge shotgun shells through a 12 gauge shotgun. Never use any ammunition other than what the firearm was designed for.
Not recommended.
The length of the chamber in a 2 3/4 inch chambered shotgun is 2 3/4". The longer 3" shotgun shells will not fit in the chamber, being 1/4" too long. You can shoot 2 3/4" shotgun shells, of the correct gauge, in a 3" chambered shotgun.
Yes
Any modern ammo should be fine. Your barrel should indicate whether you can shoot 2 3/4 or 3" shells. You may want to consult a gunsmith to see if you are able to shoot steel shot through your barrel or not.
A 41 magnum caliber revolver will shoot 410 gauge shotgun shells but is not recommended. The shot will lead the barrel rifling. There are also adaptors you can put in a shotgun that allow you to fire pistol/rifle ammunition.
A 12 gauge shotgun cannot fire 20 gauge shells.
http://www.wikihow.com/Shoot-a-Shotgun