Widener’s Guide to Smokeless Powders
Widener’s Reloading & Shooting Supply recently published a helpful introduction to reloading powders. Widener’s online Guide to Smokeless Powders shows the various types of powders, and explains how the differences in powder kernel/flake size and shape, and burn rate affect performance. We recommend you visit Widener’s website and read the Powder Guide in full.
Take a close look at these illustrations which show the key differences between the four main powder types: extruded (stick) powder, ball (spherical) powder, flattened ball powder, and flake powder.
Burn Rate Basics
Widener’s Guide to Smokeless Powders also has a useful discussion of Burn Rate (a confusing topic for many hand-loaders). Wideners explains: “While a gun powder explosion in the cartridge seems instantaneous, if you slow it down you will actually find that each powder has a different ‘burn rate’, or speed at which it ignites.” This video shows powders with two very different burn rates. Watch closely.
Different burn rates suit different cartridge types notes Widener’s: “In general a fast-burning powder is used for light bullets and low-speed pistols and shotguns. Medium-rate powders are used for magnum pistols, while high-velocity, large bore rifle cartridges will need slow powders[.]
It should be noted that burn rate does not have a standardized unit of measurement. In fact, burn rate is really only discussed in comparison to other powders; there is no universal yardstick. Specifics will change by cartridge and bullet types[.]”
You’ll find answers to these and other questions in Bryan’s book, 
