Since each rifle is an individual no person can accurately predict which powder will work best in each rifle.A load that works great in one 243 or 270 may perform very poorly in another 243 or 270 so it comes down to trial and error.Trying to load both rifles with the same powder makes things a little tougher so you may have to test several powders to get the results that you desire assuming that you can that you can get the results you want with a single powder which is not a given.It all depends how accurately you want your guns to shoot.