The fact that no cop has ever examined your magazines is a moot point.
Cops shoot at our private range all the time, and the SWAT sniper team is there at least once a month. They are professionsal, but will still laugh and joke with other shooters and examine AR15 setups and new scopes other shooters have on their black rifles. As far as I know, no one has ever been hassled over any preban/postban nonsense.
However, if a search warrant is issued for your home, for whatever reason, anything found to be in violation of the law will be stacked to get you to plea bargain. You can plan on having your computer seized and examined, your personal papers scrutinized, your gun safe gone through, etc., etc.
Play it safe and don't break the law! It's embarrasing for the local DA to kick in the door and then have to apologize for a mistake, so believe it: they will search your home and thet will find a justification for getting a judge to sign a warrant.