The barrel might be bent, which you would have to check. Is the rearsight lowering when you adjust the elevation wheel? Sometimes they don't due to the threads being knackered or the pin in the rear of the cylinder being in upside down (hollow on top part). Have you dropped the metal rearsight blade (held by 2 screws) down to lower the rearsight? On the mk2 versions, which should have this type of rearsight, the foresight post is also on a ratchet (undo the screw on the top of the sight body and lift post up). I also think that originally Bsa did 3 different post heights for the foresight.
If it is the earlier sights, then there is not much I can suggest. Always worth letting someone else try the gun to see if it is you or the gun.