I have a Mossberg 590 20" barrel. Is it possible to put on a 18.5" barrel? New tube needed? Where can I get parts? I like my shotgun, just wish it was slightly smaller. If I could convert it to SBS I would. I'm not certain here in Indiana where I live if I can register for SBS? What's the police 590's barrel length? 14"? I'll just ask about the 18.5" since that's MUCH easier... I hope. I like this 18.5" barrel adjustable model. Where could I find the barrel with the sights like this one?