These props were cast off of the ANH blaster, with the scope mount removed. The Rotj scope mount was rigged up to fit over the existing scope mount points leftover from the ANH hero.
One interesting thing to note. Some people think this was from the same casting as the Merr-Son blaster. But this isn't so. You can see the difference in the way the flash hider is oriented, the position of the safety and the position of the sight.