30 Nosler velocity vs. Freebore questions

[MagnumManiac]

The loss of velocity leads me to believe not all the powder is burning

This is a sure sign of excessive pressure, not of powder not burning.
Whenever you are ADDING powder and velocity flatlines, or decreases, is definitely excessive pressure, because the powder is now in a state of detonation, which is unstable, and you would see erratic pressure spikes even though no increase in velocity is occurring.
If you see ejector marks and swipes, STOP!

Cheers.