Cordite burn rate does depend on the thickness of the threads loaded but the idea of it is to prevent sudden increases of pressure in the barrel hence relatively slow. I found this: "Comparison to Smokeless Powders: As a rough modern approximation, cordite is often compared in performance to medium-burn rate powders like Reloader 15 (RL15)". in my 300 Rook I was not trying to duplicate a factory load (if you could even find one) so I tested all the usual suspects but found the most accurate by a long shot (is that a pun?) was 3.3 grains of AA5. In my 32 S&W Long the most accurate powder was H108 (is that the one that is compared with AA9?).
