Hmmm..
I understand your question, but imho..... I wouldnt worry about anything other than knowing what the speed is of your projectile is.
I was inquesative yrs past about getting down to the natt,s ass about chronographic readings but as time went on, I realized something: Bottom line. Once youve completed your ladder testing and develop,d an accurate/consistant load giving you .25-.50 patterns at 100 then you take that load , take 5 shot average reading from your chronograph and use that given speed as input to calculate drop and deviation via ballistic calculators. Keeping in mind to record the outside temp while chronographing.
(for me) I wouldnt worry about SD or ES especially if the propellant your runnning is showing consistant and accurate results on paper. All you can do is keep loading exact amounts of any given propellant and pray that it always burns the same rate everytime.
I hope I help,d in some way...if not?....then please excuse my rambling
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