Re: Will 223 work in a 5.56 chamber?
Actually, it's the throating. The 5.56mm and 223 Rem cases are identical. The 5.56mm ammo runs higher pressures, and can be a serious problem when fired in a 223 Rem chamber. The 5.56mm NATO chamber has a notably longer throat, which reduces start pressures. Clearly, there's some misunderstanding here on just how much these throating differences can influence pressure, turning what may be a safe load in one rifle into a danger in another, with all other chamber dimensions remaining the same.
Yes, 5.56mm ammunition can be fired in a 223 chamber, and no, it won't always lead to blown primers or catastrophic failures. But it has happened, and will continue to happen so long as people choose to disregard the warnings that have been posted both here, and in Ordnance and professional circles. Citing empirical "evidence" that, "I've done it and it was perfectly fine" is a bit like dashing across a busy freeway, making it to the far side, and declaring it to be completely safe. It ain't, and it will eventually bite you.
Heed the warnings. You're issued exactly two eyes and two sets of hands. If you want to keep them in original condition and working order, then pay attention to cautions such as this.