Actually it's the other way around, you want slower burning powders for cast bullets in rifles. The slower powders have more of a push/softer short start pressure then faster burning powders. With cast bullets that's where the games won or lost.
The front/nose of the bullet enters the rifling and starts to twist. The back of the bullet is still leaving the case and the pressure of the load is bumping the back of the bullet up in diameter to the size of the ball throat. The back of bullet seals the ball throat grabbing the sides of the bbl while the front is still twisting in the lands. Rotational torque is exerted on the bullet from this and bad things can and will happen.
I've done a lot shooting/testing with cast bullets in several different 308w bbl's/rifles. bl-c2, varget, 4064, 4895, 4320,4350,rl16, rl19, 380, leverevolution, 414, tac all work well in the 308w.
My go-to powder in the 308w is h335 for a general all around plinking powder.
Get a # of rl19 and cast up some 180gr or heavier bullets for the 308w and work loads up. You'll get impressive velocities/accuracy with that slow burning powder and heavy bullets in the 308w.