Every one I've seen were both sweated and cross-pinned. I've heard of some that were JUST pinned, but if you assume that and try to beat the sight off without heating and is IS sweated--well, you can imagine things aren't going to work out so well. You only have to heat to about 650 degrees max to break the sweat bond--nothing that will do any damage to the action or barrel, and a small plumber's torch will handle that easily without excess heat that could cause problems.
"Why is is called Common Sense when it seems so few actually possess it?"
Guns only have two enemies: Rust and Politicians.