The Mavericks have 3 different models. An all purpose model which I have has a 28" non-ported ventilated tube with an interchangeable Accu-Choke system. Then there are 2 slug models one with a rifled barrel and one with not and sorter barrels if I'm not mistaken, not sure the length though.
One way to tell which model you have is if you have rifle sights on it, then it is slug model. If you don't then it is an all purpose.
I bought mine at Walmart since I found it pretty cheap there. I have never seen a Maverick slug model in stores anywhere except in a couple gun shops.
All the Maverick barrels are interchangable with the Mossberg 500 model ones. So you can swap it out if you want to. I never saw the need to since i never have had a problem with it shooting bird shot. I might change to a shorter barrel down the road since for my taste the 28" I have is too long for slinging around for trap shooting.
I also have an old Remington bolt action magazine fed 20 guage I use that is alot more fun. It's currently apart though cuz I need to replace a few bolt parts.