Welcome to the forum.
Cast bullets cannot usually be fired to jacketed bullet velocities without a lot of special effort. If you want to do that you've got some studying ahead of you. Bore lapping (if yours isn't lapped already) and extra hard alloys in gas-checked style and high performance lubes, like LBT blue are usually involved.
In your gun, typically you would shoot jacketed bullets in the 3000 ft/s range. For cast bullets not specially made for higher velocity, you'll probably be in the 2000 ft/s range. Unfortunately, at the lower pressures used to fire cast bullets at that lower velocity, IMR 4831 is too slow burning to burn well or consistently. It also doesn't do well with reduced loads in general, and can sometimes either squib out or cause pressure spikes operating in a low case fill. It's great for full velocity jacketed bullets in .270, but not a good choice for cast bullets.
What I would recommend you do is get some IMR Trail Boss powder and follow the
instructions, here. If you want to drive them faster and use a reduced load, you can also try IMR 4759, which is bulky. If you get to really fast cast bullet loads, the slowest powder I would use is H4895. Unlike most stick powders in its burn rate range, it can be loaded down to about 60% of a max load, which ought to be somewhere around 30 grains for you. But, again, follow
the instructions.