Cast bullets need to be groove diameter except for Marlin Microgroove barrels, whence they should be .001 to 0.002 oversized.

Cast bullets must also be loaded fairly hot in order to abdurate properly. The pressure (12,000 psi or more) will crush the bullet enough to conform to the rifling. The advantage of swaged HBWCs is that they will expand to fit the rifling with very low pressure. However if you exceed about 600 fps, lead will line your barrel like Christmas tinsel.

Semi-wadcutters are just as accurate as swaged wadcutters, more accurate at longer range and higher velocity, and punch clean holes, but they have more recoil when loaded properly.

I load cast bullets to magnum pressure and velocity, with no leading up to about 1800 fps in a carbine. With a gas check, you can load up to about 2250 fps for loads that are within safe pressure limits.