You want to read the rules before you pattern a shotgun at a public range, or a club for that matter. Many ranges do not allow shotgun patterning on the rifle or pistol ranges because it chews up the target backboards very quickly, much faster than bullets do and those backboards are a big expense. My club prohibits patterning shotguns on our rifle and pistol range. We did create an area using a couple of skids strictly for patterning. It doesn't take much to make your own portable patterning board you can set out in a safe place to do your patterning.