Colorado has a 15 round limit, that went into effect several years ago, anything higher is "high capacity." The ban here does "grandfather" in magazines purchased prior to July 1, 2013. You don't have to prove anything- it's the burden of the prosecution to prove you bought them after the ban. It was this genius piece of legislation that sent Magpul and all of its jobs out of Colorado and handed them to Wyoming. I'm not sure what state the OP is asking about, but if he is in Colorado, the law here is 18-12-302 in Colorado Revised Statutes.