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.
Its amazing to me, the different things that can affect trajectory! Has anyone ever tried to compile a list?
Yes. The 1/2 completed list was published as The Bullet's Flight From Powder To Target by Franklin Mann - In 1909. The other half can be found in Phil Sharpe's Complete Guide To Handloading. Sharpe's book was published in 1937. Anyone seriously interested in shooting should read both of those books. Mann's book is fairly difficult going, since it has hundreds of tests and the results, but it is worth reading and re-reading. It was a primary source for Major General Julian Hatcher's research and development strategy as the chief of small arms development of the U.S. Ordnance department during WWII. Franklin Mann had nearly completed the second volume at the time of his death in 1916. His widow destroyed it, believing it had destroyed him - He died a bitter man, believing that nobody would ever put the fruits of his research to use... A few of the men who did put it to use were Phil Sharpe, Doug Wesson, Hatcher, Whelen...
