I have loaded and shot literally tens of thousands of rounds of .223/5.56 ammo. I have used both standard and magnum small rifle primers. I have NEVER had a slam fire. I would recommend you not use Federal primers as they tend to be the most sensitive available.
As an extra precaution, always load from the magazine. The resistance of the feed lips will slow the bolt carrier just enough to keep everything fine. If you were to drop one in the chamber and let the bolt slam on it, you MIGHT get a slam fire.
If I were in a colder climate and using ball type propellant, I would opt for a magnum primer to get the cold, hard to ignite powder going properly. In Texas, it does not get cold enough to cause problems.