At one time IMR published data for 270 - 300 grain bullets with 3031 powder for use in rifles. I've used the load once with 300 gr XTP's in a single shot rifle, and it works pretty good. 2400 always seems to give me the accuracy. I'd start with the 300 grain load data and see if that holds promise.
Lyman lists a 275 grain SWC cast of linotype with 2400 they list 17.6 grains to a max of 20.4 grains. Alliant shows 2400 with a 265 grain jacketed flat point with a max load of 17.0 grains.
So if it were me, my guns, and my personal safety, I'd try 17.0 grains of 2400, and not go over about 18.8 or 19.2 grains, depending on how things felt, looked and seemed.
Be careful, and you should end up with a very doable combo.
Keith