I step down necks with .020+" in 3 steps, just to eliminate any possible crushing issues. If you are doing 100 cases, this doesn't take any time at all. Just lube the necks. I do 7mm (.284") to 6.5mm (.264") all the time with various wildcat brass like the Sherman Short Mag lines. But for .264" to .257", I do a single pass.
I have done hundreds of 6.5CM to 6CM brass this way. Lapua brass mostly.
.264 (virgin necks are probably .289 OD neck) to .243 (.271 OD neck), remembering necks will thicken going down, I would go:
.283"
.277"
.271"
Then run a .241 mandrel back up through.
Finally, trim and square up the necks and chamfer in/out.