BB........you might try the Partition 220 semi RN, they are supposed to shoot well and you should be able to get an easy 2800 out of them. No worries about them coming apart........Doubt you'll ever recover one though........I suspect they will go brisket to butt hole through anything NA has to offer.
Like I said I had the best results both accuracy and velocity wise with IMR 7828 in 3 or 4 different 300 WM.........I have also found the best accuracy at red line in all 300s I have loaded for, unfortunately some of the very best groups shot, the brass would no longer hold a primer after one load......You might see a significant tightening of groups if you keep going up and watching for pressure signs........RL19 and IMR 4831 I consider too fast for 180gn + bullets in the 300 but you may wish to put some more H1000 and see how it does. Another trick is to put some electrical tape in a pad at the forend tip and try to apply 5-10 lbs upward pressure on your barrel. This has worked at least 80% of the time for me in tightening groups with a sporter weight barrel.