I've tried forming some .256 Winchester brass from new .357 Remington brass, but it seems rather hard in the mouth area and forming has been largely unsuccessful (even using some intermediate dies to do it a little at a time). Is WW or Federal brass more ductile in this caliber? Would appreciate the experience of anyone who has been successful.

what do you think about standing them in a pan of water with just very little of the mouth showing above the water and lightly annealing them?

I've found nickel cases harder to form. You can also use a 30 mauser (or 30 Luger) die to just start the process too. Also found if cases are warmed to form better...I call it drawing them and only the neck/mouth area.

There is a simpler way if you cast: dip the brass cases in a pot of lead alloy. The lead won't stick to them, and just a few seconds in the alloy will anneal them quite well.

join the club - i've never been successful at forming them either