Contenders many times have a left hand twist. This causes movement to the erecter tube. I had a heavy recoil 35 caliber contender barrel that would only shoot 3" groups at 100 yards. I rotated the scope 90 degree CCW and the it started shooting 3/4" groups. The reason for a the problem is simple. A left hand twist makes the gun torque to the right. When the scope moves to the right, the erecter tube has to compress the leaf spring. On a right hand twist the erecter tube pushes against the adjustments under recoil. When you rotate the scope you go by the RUUL when adjusting the scope. RUUL simply means right is up, and up is left.
Michael