The WASP coating is a process called "salt bath ferritic nitrocarburizing". Some info on it can be found here:
http://en.wikipedia.org/wiki/Ferritic_nitrocarburizing
Here is what CMMG has to say about it on their website:
http://www.cmmginc.com/pdfs/WASPTechSheet.pdf
After reading the technical information from CMMGs website, many people have probably wanted to ask "If the WASP finish is better than chrome-lining, why do you only apply it to your lower-end LE series uppers?". Though I
haven't asked, I suspect the reason for that is the demand for Mil-Spec uppers, and the military specification for carbine barrels is chrome lining, not salt bath ferritic nitrocarburizing.
I am not a metalurgist, and cannot tell you which one is better than the other, but the truth is probably that they are both good, and the reason for the demand of Mil-Spec uppers is the popular assumption that if the military uses it, it must be the best. But, when you consider how many years Gore-Tex was in use by civilians before the military ever
considered adopting it for use in combat uniforms, that assumption no longer holds water. In fact, the public is often the beta test group for products eventually adopted for military use. In which case, we have the good stuff before they do.
One interesting thing to note is that many people feel piston ARs are the pinnacle of performance when it comes to carbines of that platform, and of the 25-30 different uppers CMMG manufactures, only two are piston operated, and one of
them has the WASP finish.
If I was a bettin' man, I'd say that CMMG came up with the idea of the WASP coating because it was more cost-effective than chrome-lining, and allows them to market their products to folks who are looking for a lower-cost AR-15 without compromising quality by using chrome-moly barrels that have not coating or lining at all, while still giving the Mil-Spec addicts what they demand in their more expensive line of carbines and uppers.