Speaking softs only, pretty much any bullet that goes into and out of a die has some taper in the parallel section of the die. Generally from .0002" to .0004". Without it, you will play hell getting the bullet out of the die. That is not necessarily on the whole bullet. That would depend on the weight of the bullet and the length of that bullet's parallel section, i.e., out of the same die, a 308-150 will have less total taper than a 308-200 just because the straight section is shorter. No taper on the solids.

I know that a TBBC soft will bump some but, with that big contact surface area, it doesn't need to. Tony has fired some smooth sided Xs in his double (collective gasp ). He sent me a barrel slug and the bullet. His barrel slugged .4095". The bullet was .4073. The accuracy was fine. Pressure and stress wise, he got away with doing so because of the great disparity in barrel/bullet measurements. At his pressures, I doubt the bullet bumped but still with that great surface, it didn't need to. And he has very narrow rifling lands just like yours.