OK, I have a 7-shot Mossberg 500 12ga. I would like to turn it into a hunting shotgun that can use a longer than 20" choked barrel.

From what I understand, I will have to change the barrel AND the magazine tube, correct?

Will I also need to get a new mag spring, end-knob (hopefully one with a built-in swivel/sling), and mag follower?

Any suggestions on what to get parts-wise, what length barrel and what kind of tube? This will be mostly or small-game and bird hunting, though I suppose buckshot deer hunting or with slugs (rifled barrel eventually?) could be in order in the future.

For the cost of all the parts involved you would be better off getting another shotgun or tradong that one in on another one.
Ben