So far the load data I've seen using Magpro and the Berger 140 has a COAL of 3.250". Are you at max loads when crushing powder? Makes me wonder how far off the lands you are and if you could seat out closer to 3.390". The book max is already at 64k PSI. So I'd be careful. Just some food for thought.
I believe by seating the bullet further out past what the manual suggests would decrease the pressure because you have more volume now. Correct me if i'm wrong.
I noticed a slight decrease in velocity when I started playing with seating depth and seating further than what the book said.
I would still caution anyone to tread lightly when approaching or exceeding max loads.