The 223 Wylde is a hybrid rifle chamber that allows you to safely fire both .223 Remington and 5.56 NATO ammunition. It's designed to improve accuracy and reliability.
How it works
The 223 Wylde has the same chamber angling as a 5.56×45 rifle, but a tighter freebore diameter.
The tighter freebore diameter of the 223 Remington improves accuracy.
The sharper angle neck of 5.56 NATO improves reliability.
Why it's used
The 223 Wylde is used by rifle manufacturers who sell "National Match" configuration AR-15 rifles, barrels, and upper receivers.
It's also a popular choice for competitive shooting where precision is important.
History
The 223 Wylde was pioneered by gunsmith Bill Wylde.
It was designed to address the discrepancies between the two popular calibers without compromising on performance or safety.
There's no such thing as a "Wylde .308" ammo, as the term "Wylde" typically refers to a specific chambering modification for .223/5.56 NATO, not .308. The .308 Winchester (or 7.62x51mm NATO) is a standard cartridge, and there's no need for a "Wylde" version of it.

.223 Wylde is a caliber where .223 and 5.56 can both be used without issue. It was designed for competition as it is more accurate when shooting it. There is no need for a .308 Wylde as .308 and 7.62 are the exact same ammunition unlike .223 and 5.56.

Hi James and welcome. As far as the calibers, 5.56 is higher pressure than .223 and it is the opposite for .308 as it is higher pressure than 7.62 x 51. A wylde chamber splits the difference in 5.56 and .223 head spacing so accuracy is improved when firing .223 from a wylde barrel as opposed to lower .223 accuracy from a 5.56 barrel. Cheers, stay safe and enjoy!