"And wrong"
Really.
One of the things that I learned at Test Pilot School is that Bumblebees can't fly. They don't have the power to weight ratio needed for controlled heavier than air flight in ground effect, never mind being able to perform out of groud effect hover.
Empirical evidence indicates otherwise......
And:
Millions of rounds of surplus 5.56 shot thru .223's for decades without mishap indicates otherwise as well. Lawyers, naurally, might disagree. Especially SAAMI lawyers. Willie will rely on his observations that Bumblebees do indeed fly, and that .223 and 5.56 are the same for any practical purpose. They were the same for 40 years: Only recently have they been discovered to be different, to the endless amusement of those who have been around the cartridge since the 1960's.
Now: If you're truly worried, have your gunsmith finger-spin a 5.56 chambering reamer into your rifle for a few seconds and forget about it.
Challenge: If anyone can provide a reliable citation here, with reliable evidence based on correctly researched post mishap investigation conducted by a formally qualified forensic material analysis authority, of any modern factory .223 rifle being damaged by shooting properly loaded quality 5.56mm NATO ammunuition, I'll send them $100 by Paypal, and you can have bragging rights. Willie puts his money where his mouth is. Saying "I heard my buddy say" or "I read someplace" isn't going to cut it. Having a formal lab report specifying that there was a material failure in a factory rifle chambered in .223 produced by firing a factory loaded NATO spec 5.56mm cartridge, where neither rifle nor cartridge was defective ab-initio would do. Tell you what, submit your formal evidence here and I'll let three Moderators be the judges as to the quality of the evidence and if they agree, you can carry Willies money home.
Don't spend it yet, because it's not happened..... ever.
Willie
.