Use a butane torch to heat the sight only. Loctite will melt with the heat. The cheaper butane torch will heat up the sight base and not bother your barrel any. I am talking put the flame on the base for about 3-5 seconds then try to take the screw out. Repeat as necessary. Should come out no problem if loctite. If rusted in, breakfree or hot water will be your best bets.

Steve laugh