Hi, I'm a first time user. I am planning on purchasing a Mossberg 500 Persuader, with an 8-shot magazine and 20" barrel. I would like to also purchase a 28" barrel for use with this weapon, but the one I found on www.mossberg.com and also www.cabelas.com appears to only be for the 6-shot Mossberg. Is there a way to fit it? I have very little experience with shotguns so any advice would be greatly appreciated. Thanks.