Thats the burning rate at ignition of the outer layers of the grain. Due to totally different surface treatment these values are not comparable. There exists no single "burn-rate" for any surface treated propellant (other than "green-corn" which is not available to handloaders).
"A stupid man's report of what a clever man says can never be accurate, because he unconsciously translates what he hears into something he can understand." Bertrand Russell
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