[pblanc]

The main difference between the typical .223 Remington chamber and the 5.56x45 chamber is the length and volume of the leade, or throat space. The 223 chamber is tighter with a shorter leade cut at a steeper angle compared to the longer leade of the 5.56 chamber which is cut at a shallower angle. The freebore diameter of the 223 Rem chamber is also about .002" less than that of the 5.56 chamber.

I said "typical" because there is no absolute uniform standard for either chamber dimension as multiple different reamers have been used by different barrel manufacturers.

The more generous chamber throat dimensions of the 5.56 were necessary to accommodate some of the longer military projectiles such as tracer ammunition without causing an over-pressure situation. But the larger chamber does result in some potential loss of accuracy when .223 Remington ammunition is shot in 5.56 chambered barrels. A tighter chamber will generally provide better accuracy so long as the chamber is not so tight as to result in over-pressure with the intended ammunition or interfere with feeding and extraction.

The 223 Wylde chamber is a hybrid between the 223 Rem and 5.56 chambers. It has the longer leade of the 5.56 chamber so 5.56 ammunition can be shot without resultant potential over-pressure. But it has the tighter .2240" freebore diamter of the 223 Rem chamber. The result is a potential gain in accuracy when shooting 223 Remington ammunition, or even the more common 55 and 62 grain 5.56x45 ammunition.

I say "potential" accuracy gain because there are a lot of other factors that will determine accuracy of a barrel apart from exact chamber dimensions.