Most charts don’t show how much faster one powder is than an adjacent powder in the chart; they may be virtually the same, or they may differ quite a bit, we don’t know. These charts are interesting, but they shouldn’t be used as a definitive guide to powder performance - IMO anyway.
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Your points are well taken, and you are correct. However, two good charts are exceptions to the statement above, and are my favorites for that reason: the Western Powders chart, and the Lapua chart. I keep that Western chart on my reloading room wall, although I do wish they'd update it with the newest powders.
As mentioned above, burn rates are not absolutes, but the Western chart gives a pretty good visual of the relative burn rate compared to other powders.
https://www.accuratepowder.com/wp-content/uploads/2010/12/burn_rates.pdfhttp://bulletin.accurateshooter.com/2014/01/powder-watch-n133-lt-32-and-norma-powders-available-now/
