Talked to Tommy at Leadheads. He claims there is no need to do anything but the following.

300gr bullet use 51gr of IMR 3031

425gr bullet use 40gr of IMR 3031

Any mention I made of trying something else he says will be a waste of my time. I find it hard to believe but old buggers are rarely wrong. I'm going to try that set up. This is the first time I wished I had a Chrono.

Tom