Here is a link to the page on Goex express on Goex's web page. I think it is like Pyrodex SELECT or JIM SHOCKEYS PREMIUM GOLD. It is just a finer more consistant form of the original powder.

http://www.goexpowder.com/product-express.html

if you ever examined Pyrodex RS and Pyrodex Select.. the same grade of powder mind you just screened a few more times so that the grain size are more uniform. I think this is the same case here. They take a standard Goex and screen it a few more times to make all the grains the same, then charge more for it. I could be wrong. It might be something totally different. On my next order I will have to get a can or two and try.