Yes, I have swaged bullets up and down to fit a particular bore. Swaging a .458 bullet up to .470 might be possible, but a better way might be to swage a .474 bullet down to 470. Look at .475 pistol bullets for your BP express. Call Corbin; they are the biggest bullet swaging equipment company on earth. Not cheap though. Cast bullets is the way I would go. Check NEI if they are still in business; they used to make all sizes of bullet molds. Other guys will make custom molds too.