From the new 795 Mega Thread
Note: To remove the rear factory sight
1 Lift up the sight
2 Pull the sight ladder out from the middle toward the front
3 With a small wood or plastic dowel drift the rear sights dove tail out. Left to Right
Make sure you do steps 1 and 2 first so the sight isn't fighting your. The Dovetail has a slight tapper to it. It is tighter on the left side and explains why you are having a hard time.
What I do is fully strip the upper, bolt and handle.
Then I sit on a carpeted floor indian style. With my foot or knee I try to hold down the receiver. I then use a dowel to direct the motion of the hit. (Personally I use my county comm kubaton http://www.countycomm.com/kubo.html
it works reaaally good!)
You may want to take the rear sight off all the way to the right and then put it back on. The momentum might help it move. This is what I do when I can't get it to budge. You may even have to use a jewelers file just a tiny bit. TINY! there is no adding material back! Just touching up a bur or groove.
BTW you might want to order the Factory Upgrade Rear Adjustable Sight and just replace the one you have. Its a good upgrade for 10 bucks!