I have a Savage/Stevens mod 87 22Auto rifle. Nice little gun about 70 years old. Shooting it, it shoots about 6" high at 20 yards. This is with the rear sight resting on the barrel, low as it will go. I understand there is a way to figure how much taller front sight I need but I don't know how to do it. It is 22" between the front and rear sight. Can someone help? Wallacem inGa