This is a thread dating back to 2009 on the subject where some good points are made. Here is a quote from an old VitaVuori reloading pamphlet which precedes their burn rate chart. "Current cannister powders in order of
approximate burning rate. This list is approximate only and
not to be used for developing loads". My career for the most part was devoted to test engineering but I have no clue as to how burn rate testing of cannister smokeless powder is performed. I simply cannot find a published test procedure or method. The link I posted allures to that. SAAMI, ANSI or any others list a test method and procedure. Every now and then a list is published normally adding new powders and removing powders no longer in production. Even looking at current list, as mentioned, list are not always in agreement. Obviously using a powder burn rate chart for load development is not a good idea. From time of ignition to bullet exiting the case is pretty quick, in many cartridges including rifle ignition to bullet exit barrel is 0.002 seconds and often much less. There is a whole lot happening in a real short time interval. Today's electronics using chamber pressure sensors is really pretty cool stuff. Rather than measuring a copper slug compression we can actually plot the pressure curve and note how fast a powder reaches peak pressure. I would stick with published load data.
Anyway if anyone had some good and credible dope on how burn rates are actually measured I would really like to read what you have.
Ron