Find some old gun parts....a bunch of screws, bolts, etc. Keep them. When uncle sam shows up at your door to confiscate your weapons, give them the parts and exclaim when you heard guns were illegal and may kill someone, you immediately disassembled them so they would cause no harm. Give them a few spent casings, gasp and cry that you were so troubled that you threw away most of the parts and this is all you have left.
Hell, bury a few parts outside. Dig them up and turn them in. Cry. Be remorsful. Beg for a card so you can call if you find out anyone has a gun. Make sure you have a "greenpeace" sticker or some other liberal token readily available. Nothing says "I hate guns" more than the correct bumper stickers. Lament we have too many killings each year at the expense of people with too many guns. Congratulate them on "saving lives". Ask if they think mace is safe.....Offer it to them. If you really want to throw it in thier collective faces, volunteer your pressure cooker to be confiscated.
Get your story. A good story will throw the scent off you.