Some people will go to great lengths to construct conspiracy theories. The 9/11 types are a recent excellent example, and we are seeing the same sort of thing here.
The fact remains that while there are meaningfull technical differences, in casual discussion .223 and 5.56 are often used interchangeably. This matters little to the dedicated conspiracy theorist, who often doesn’t know enough about the hardware to realize you could probably shoot quite a lot of 5.56 is a .223 spec firearm without incident, despite the fact that doing so is not advisable.
I usually wait a few months do let the facts dribble out on things like this before I decide who’s lying and who’s telling the truth. So I am relatively uninformed about the Sandy Hook shooting. Quite frankly it is just to horrible to think about right now. So I am not part of any conspiracy or cover up. Just bringing FACTUAL info into the thread. Now as for shooting a 556 round in a rifle designed for a 223 I will take your word on that. I do not own either a 556 or a 223 so I don’t know if that is a common practice or not. I’ll just go back to lurking. :)