You can find lots of info on the site,
www.perfectunion.com Its is a mini site mostly and the guys there will help you if you give them a chance. And your gun should be getting at least a 3" or better group at a hundred. My 580 series with the tapered barrel will do that with cheap Monark ammo from Academy sports.
Like others said check your screws and sights and most important is to make sure your gas port /fore end cap is even on both sides and evenly torqued down. That seems to be one of the biggest things to make accuracy not so good. You want the gap between the top and bottom pieces to be even.