For 180gr XBT bullets and 300Win mag, the barnes manual says

RL22 70.5gr to 75.5gr (2898fps to 3103fps)

so Barnes claims tsx is safe 2gr over this load. So you should safely be able to go to 77.5gr. I have found with most of my magnums (powder greater than 70gr), you can got 3.5gr or so before heavy bolt lift.

I bet your not up to pressure yet, until your brass is not trimmed or your smacked into the rifling. Maybe even soft primers. Like I said, it depends which one. Watch for bolt lift.