The big difference in chambers is in the distance the bullet has to "jump" from case mouth until it reaches grooves of the rifling. That distance is free bore + leade. It also depends on bullet ogive and seating depth, but those factors can be adjusted (to the extent the magazine will allow) if you reload. Anyway, 5.56 uses a long leade to handle the higher pressures. The Wylde chamber retains that longer leade, so it's still safe to operate at 5.56 pressures. However, it uses the shorter free bore of the .223 Remington chamber.
Example:
.223 has a free bore of .040" and a leade of .045" Total distance from case mouth to rifling is .085"
5.56 has a free bore of .073" and a leade of .164" making total distance .237.
If the chamber is a true Wylde chamber, it should have a .040 free bore and a .164 leade, reducing the total distance to .204"
As mentioned, actual dimensions may vary slightly from one manufacturer to another. It also depends on how badly the chamber reamer is worn out before its replaced, but thats a whole different topic.
The bottom-line takeaway message that I get from this is that the 5.56 chamber is not necessarily designed for maximizing accuracy, its designed to handle a little more pressure and a lot more fouling from heavy usage. The chamber I choose would depend on the intended purpose of the rifle. If its a battle rifle, plinker, or general purpose sewer tube, 5.56 wins. If its going to be a precision target/varmint rifle, I'd go with .223. If its going to be a varmint/plinker that may see some occasional 5.56 ammo, I'd go with a Wylde.
That's just my opinion on the matter - take it for what its worth!
