So, by now everybody must know that H110 and W296 are exactly the same powder. But if that's so, then why, when people test them, do they get different numbers? Well, if you look at the micrographs below, you will see that while the average size of the powder grains is about 0.45 mm, even a small sample contains grains between 0.3 and 0.6 mm. All particles are almost exactly 0.18 mm thick because they are flattened between rollers separated by 0.18 mm. I'm sure you've all noted what happens when you shake or tumble sand or ground pepper... It tends to segregate with the largest particles rising to the top. This occurs via a well understood phenomenon called Granular Convection. Well, that's pretty much it in a nutshell. And it accounts for most variation that you observe when testing two different canisters of powder. Phil Sharpe pointed this out sometime in the early 30's, and he recommended sifting out the smallest particles of powder to improve grouping. It's still true today.