Try this. Remove the stock. Open the bolt & lay the barreled action on its right side on a firm surface like a 2x8. Lube the rear sight with WD40 or something similar. Take a .4" or larger brass or aluminum punch (end must be flat) and lay it along the very bottom of the sight base - not on the side. The base is staked on & you must use force to break the staking. With a 2 lb or 3 lb hammer, hit the punch smartly. The sight should come off in 1-3 strikes. I've removed dozens of rear sights like this, usually dry, no lube & didn't bend or break any.