The Wylde chamber will safely digest both civilian .223 and military 5.56.

"The .223 Wylde hybrid chamber was designed by Bill Wylde of Greenup, Illinois, to exploit the accuracy advantages of the .223 Remington chambering without pressure problems or compromising the functional reliability of semi-auto weapons like the AR-15 family when using 5.56×45mm NATO military ammunition.[2] Coincidentally, it shoots the relatively long and heavy 80-grain (5.18 g) bullets commonly used in the Sport Rifle Competition very well and is one of the preferred chambers for that use. The Wylde chamber is used by a few rifle manufacturers who sell "National Match" configuration AR-15 rifles, barrels, and upper receivers."

The way Bill Wylde tells the story, is that the chamber was designed for single loading, long competition rounds.
It was dumb luck that the new chamber shot everything well.