Pretty close only counts with horseshoes and hand grenades
Taking a percentage is not precise enough with powders especially those with different burn rates, it is not completely linear, plus as Fred mentions there are many other variables at play.
Obviously you are one of those who labor under the misapprehension that anyone who publishes reloading manuals, whether it is a powder maker, bullet manufacturer or a bullet mold maker,
actually shoots every load they list in their manuals! They do not! They fire often only one load to establish base velocity and pressure and then extrapolate/interpolate from that base figure! Why do you think Sierra shows velocities in 100 FPS increments? Or just why many manuals reduce the maximum load by exactly 10% to arrive at the starting load?
Go back and READ my original post, and those of others who conformed from their own results
that it works! Contrary to what you stated most propellants
are linear to a great extent. You infer that in some way interpolating a load between a published minimum/maximum could be some way dangerous! This is absolute BS!!!!
And, if you had READ my original post you would have seen that I said absolutely nothing about making estimates between propellants of different burning rates! All I said referred strictly to specific powders the OP asked about,
and was supported by chronographed data IN MY GUN! There was a disclaimer inferred about his barrel length varying from mine. AND, the "Close Enough" only referred to the velocity
estimate calculated by the formula. There was no mention of pressure whatsoever, but do you really believe that reducing a load does anything other than reducing velocity and pressure at the same time?
And, a final disclaimer. The formula shown is truly specific to single-base propellants. Double-base propellants are not strictly as linear in their performance as single-base, but, again, close enough when
interpolating reduced loads.
The formula referenced is not mine, it came from sources published by
Dupont many years ago. Maybe you would like to argue that the technicians and engineers at Dupont don't/didn't know what they were talking about!!!!!!!!!!
Unfortunately your opinion used to be something I respected, but no longer!