So just to be clear Rich, you experienced no noticeable malfunctions, no rounds that were not normal, nothing that would indicate a squib? You would have noticed a squib, followed by the next round destroying your muzzle brake, but we haven't heard enough detail(s) to reliably diagnose from the situation described...given the pressures of a .223 combined with the projectile velocity, a squib seems unlikely without some noticeable clues...?
I asked about the brake due to casting porosity, which can make a cast piece of metal (any metal) far weaker than the same metal without gap-bubbles in the cast piece. If the brake is milled from billet, porosity is not an issue. If the brake is cast, it is a possibility for a weakened piece (brake). I'm inclined to believe a muzzle brake is milled...if there were porosity it is likely to have been discovered during the grinding process of the brake, but you never know.