The patch with oil on it helps to remove left over solvents and provides a layer of corrosion protection if the gun is to be stored.The dry patch removes almost all of the oil.You should always remove as much of the oil as possible before firing the rifle.Some people do not dry swab the barrel before firing and large amounts of oil remain in the barrel.This situation is where pressures can climb and problems can arise.If you properly dry swab the barrel before firing there isnot enough oil left in the barrel to cause problems.