A stray round in checked luggage can cause considerable difficulty if it is not in a factory box, and there is no spare hole in one of your factory boxes in which to put it. Written reports to the local PD, TSA and airline ... and an offer from the airline to "store the round until you return from the trip".
I'm afraid that these rounds were not in the checked bags, they were in the carry on. As they say, you learn something new everyday. It's just a harder lesson on some days.