I like to visit http://gun-deals.com/ammo.php and do a quick search and sort before making large purchases. If you know of good places to buy ammo that aren't listed - then add them to the database, too. The more people that use this resource, the more valuable it is. It's showing 93 deals for .223/5.56 right now. And no, I'm not affiliated with the website, just a fan of a helpful free site.