ORIGINAL: cayugad
To remove it, this is an adjustable, push down on the rear sight and take the elevation adjustment scew out. The sight then opens up. Inside under the elevation bar you will see the screw that locks the sight to the barrel. Just take that out and the sight lifts off the barrel.
Actually it depends on the ageof the rear sight...on the early style rear sight, removing the elevation adjusting screw still won't allow the top half of the sight to pivot up, as it is still captive at the back end due to an overhang.
On those, the pivot roll pin itself alsohas tobe drifted out in order to remove the top half of the sight...then the two basemounting screws that hold the sight base to the barrel will be exposed and can be removed.