I had a similar problem when I removed the front sight from my stainless Mini-30. I heated up the front sight with one of those grill-starter devices that you click and a little flame comes out the long end. I suppose a cigarette lighter would accomplish the same thing. Anyway, I let it get hot for about 30-45 seconds, then gently tapped off the front sight with a ball peen hammer and a piece of wood. It popped off easily, and I noticed some sort of Locktite-type adhesive between the sight and the barrel.
The flame left a blackened mark on the bottom of the sight. Fortunately, the flame didn't mark the barrel. In hindsight, I should have wrapped some aluminum foil around that area to keep off the soot.
I have no idea how a flame might affect bluing if you have a blued barrel. Maybe the aluminum foil idea would work for a blued barrel too.