Don't know why .223 or 5.56 round won't load from the mag. My ar's are chambered for the wylde and load fine and will shoot sub .5 moa. Maybe that's one persons's opinion that is only talking about BR shooting. Don't know why he would make that type of statement for having a wylde chamber. Here's an opinion from Sniper Central.
"The .223 has a tighter chamber around the neck and is shorter which allows for a bit better accuracy. You can shoot .223 ammo in a 5.56 chamber, but it is DANGEROUS to shoot 5.56 (surplus for instance) ammo in a .223 chamber. BE CAREFUL. What the Wylde chamber does is allow for 5.56 ammo with slightly tighter chamber for better accuracy. So you can shoot both 5.56 and 223 safely with good accuracy."