agree. just because your POI increased drastically doesn't mean you had a drastic change in velocity. I have seen this just doing a load workup. 1 node would print high and the next would print low. (as much as 1.1 mils at 100yds) and the "scatter node" between would have huge vertical dispersion. one gentleman explained it in a very simple way. when your shooting the barrel is whipping some barrels will whip top to bottom (most common due to the mass of the barrel wanting to rest in the lower positon) and others will go corner to corner, ect.... but when were chasing a node were trying to get the bullet to leave the barrel when the barrel is slowing to change direction in the opposite way of it's deflection. the worst point for the bullet to leave is when the barrel is back at it's rest position (opposite of what I thought) because the barrel is at its highest velocity in the arc or movement so if you add your es/sd into this a bullet that leaves those few milliseconds earlier will be in a far different location than the last, and next. look at it as a AC sine wave (analog) there is more dwell time on the peaks than the transition so that what were shooting for. and like mentioned above the brake can change that whipping both by the addition of mass as well as the harmonics, and lastly the way the gasses act on the atmosphere could impact whats going on.
a better method if you chose not to get a chrono would be to re-zero with the brake and shoot at distance and reverse interpolate the data. ie. with a bullet of x BC that drops x MOA/Mil's at x distance the velocity is roughly x fps. 300-500 yds would be a good baseline as it will be more measurable. and find the center of the group to base you calculations. ie. if 5 shots have a vertical dispersion of 5" measure down 2.5" factor that into your dialed elevation. a lower vertical dispersion will also give you an idea of how your ES/SD is. reason I mention 300-500 yds is this gives you a better idea of whats going on as there is more measureable difference. and some high bc bullets have to "go to sleep" and can have some strange results at shorter distances. ie. shoot moa at 100 yds and 1/2 moa at 200.
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