I googled it and what i gather is that its a version of the .223 chambering that is "roomier" than the others.Will
will chamber .223 and 5.56 as well.Again, that just what i gathered from it.
I don't know the specifics of it, but it's something different with the throat. It allows you to shoot both 5.56 and .223, but is extremely accurate. Think of it as a match grade 5.56.
I have a Wylde chamber in a Rock River A4 varmint. I can say that the throat is much shorter than my Olympic SUM.
I had a problem with some reloads (55 grain Hornady soft points) that were too long to chamber in the Wylde but where fine in a standard chamber. This just meant the bullet had to be seated deeper, and now they shoot fine.
From Rock River's website
Quote: The .223 Wylde chamber was designed as a match chambering for semi-automatic rifles. It will accomodate both .223 Rem and 5.56mm NATO ammunition. It is relieved in the case body to aid in extraction and features a shorter throat for improved accuracy.