How to explain velocity decrease with lower COAL + more powder?

[Certaindeaf]

Are you using the same gun?

 

[WillametteWill]

The .01 COL seems too minor to be a significant factor. Agree with others; different chrono, possibly different powder lots, was each powder throw weighed (I don't for pistol but sometimes the powder measurer wanders)...several things could add up to the 6% difference. Good question though.

 

[Member 5605]

You loaded different days. Different temps, humidity et al.

load the ladders the same day, shoot alternating ladders or stagger the rounds. You'll find your new tests don't match your old ones.