The only reason I could see for sawing off a shotgun barel, would be if you were going to use it for close range home defense. Basically ruining a good gun and restricting what you can do with it.

What he has now is a 28 inch barrel on a Rem 1100, good the way it is with the right choke and shells.

As for legality, check your local laws on using something other than a shotgun, or black powder shotgun for turkey hunting.