I had the same thing Broke referred to with a NEW rifle. I had it checked by a gunsmith, and live rounds (when we could extract them from the chamber) would clearly have the lands engraved into the ogive.
Although you periodically check your length to ogive, you also only have periodic pierced primers. I would inspect the entire lot of ammo, and see if you are getting occasional oddities in seating depth. This would certainly change your pressures. I had a lot of ammo do precisely that, and some times my ogive would vary by 50 thousandths..certainly enough to cause presure spikes.
If you do find oddities in seating depth, it can be from:
1. using brass that has various firings on it, hence varying neck tension
2. dirt inside the bullet seating cup, or die
3. dirt inside the groove of your shell holder (it holds off center some times, and straight other times)
4. using bullets that aren't consistent
5. varying the way you seat your bullets. You have to seat each bullet in a lot exactly the same way. I used to rotate the cartridge while seating the bullet, then I found that this causes both excessive runout, and varying seating depth.
6. using anything other than one consistent stroke on the press handle.
But my first guess is that there is an interrelationship between the new barrel's throat, seating depth, and powder charge. Velocity should tell you where you are relative to the max recommended charge, but even at that, each rifle is it's own rule. The max in my rifle may be 20% more or less than in your rifle. Let me know if you need to use a chrono.
