I had never experienced any problem shooting 5.56 out of a .223. This was limited to Remingtons, Savages and Winchesters firing Lake City 193 and 855. Sure, I read the "don't shoot 5.56 out of .223" but I'd ignored it.
...and I still ignore it for the most part.
A few years back Bushmaster built a batch of AR rifles marked .223. I ignored it.
Here are the results. On the left is Lake City 855 fired from the Bushmaster. On the Right is the same ammunition fired from a Colt 601.
A few minutes with a 5.56 chamber reamer and no more blown primers.