Interesting, I have not looked at the Berger data.
I don't have a 300 weatherby mag but the charge seems a little low. Alliant shows the 85g max for the 200g speer sp and RL25. The RL22 load is in the upper 70's. I would not think that the Berger bullet would make that much of a change but you never know.
Alliant Powder - Reloader's Guide
You should be seeing more velocity than you are though. I would try a different chronograph if available.I was out the other day and it was overcast and a little late and my chrony was reading quite low. Replaced the battery, better light earlier in the day and day later picked up 200fps with the same rifle and load.