"5.56 barrels can take more pressure than .223." Not necessarily. It all depends on the diameter and strength of the barrels. Furthermore, failures because of excessive chamber pressure almost always result in shell case failures with massive amounts of gas released into the action causing severe damage. Split barrels at the chamber or sheared bolt locking lugs are hardly ever encountered. Again, please stop posting erroneous information.
"Shoot enough 5.56 in your .223 and you may start blowing primers." Yes, you finally got one right! You might also see ejector pin holes marks on the shell case head wherein cartridge brass has flowed back into that hole because of excessive chamber pressure.
"Just my two cents." Your two cents isn't worth a plugged nickel. Two of your three statements were not true. Keep in mind that there could be people on this forum gullible enough to believe your nonsense and get into serious trouble.
All posters have a responsibility to be factual and or identify their speculations as speculation without supporting facts or references.
Opinions are also appropriate if they are labeled as such. Everyone has the right to make a fool of themselves in public or this forum. You are off to a good start.
Read Patrick Sweeney’s ‘The AR-15’, chapter 4. ‘Ammunition’ and his writing on barrels and pressure testing.
He says the same things, although he does explain them much better.
Then you can climb down from your high horse.
And see ‘Gunsmithing the AR-15’, Sweeney, Chapt. 3 ‘.223 or 5.56’.