I've also never actually heard of a single person having a problem shooting 5.56 in a ".223" chamber. Nobody will actively endorse it, but it's just one of those things.
I also wholeheartedly agree that a .223 is a much better buy than the Hornet, unless you just want the novelty of the Hornet. It is easy to download the .223 to Hornet velocities and you'll use about the same amount of powder and cases will last practically forever. But, you can't upload the Hornet to anywhere near .223 levels, and when you start to even try you'll be replacing cases every few loads.