Do not use on small sight or scope screws, or the head may wring off when attempting to remove. Larger hard screws, such as stock screws can often be removed with common hand tools, but may require the application of 400 degree heat to soften the compound. A soldering iron applied to the head of the screw will heat it enough. Red can also be used under scope rails, on scope mounts where the grip the grooves, or where ever you need a good mating surface between two parts. Green is a medium strength that is thin enough to wick its way into assembled parts.
Results are variable, depending how well it penetrates, and how clean the parts are.
You can try this if you don't want to remove the parts for some reason. It does not work, you will just have to take it apart, clean, and use one of the other grades. Another compound that is getting good press is Goop, available at Wal-Mart and many auto stores like AutoZone, etc. It can be used to secure loose scope mounts. It is flexible and resists lateral shock well.