Depends. You want the grooves to be deep enough not to bottom out on the lands after sizing down that much. Then you need to have the bullet lubed before reducing so you don't close the grooves up. Then you have to also have to make sure that the bullet is not sized off center. Push through nose first dies (Lee) usually are the way to go.
With all that said, you may wish to consider a custom mold from mountain molds. He can cut a 270 mold that has a .271 diameter that should work from the get go. Single cavity aluminums are $60 + shipping - not that much more than a Lyman mould.
