Another alternative which definitely works is phosphoric acid. This is often a constituent of rust removing chemicals and can also be bought in gallon containers from companies which supply cleaning chemicals. It is a powerful acid and can also be used for removing limescale from surfaces. Usually it is diluted with water before use. The objects being cleaned are submerged in the solution and should only be left in the acid for the bare minimum of time to dissolve the rust, otherwise the acid will start to dissolve the underlying metal! I have cleaned an old vice pillar drill vice belonging to my grandfather which developed a thick layer of rust after being exposed to dampness in a shed for over thirty years and the acid completely removed the rust.
Once you remove the rust, rub some oil into them and wipe off any excess. This will help to prevent future corrosion.
Sand can also be used as an abrasive for removing rust from tools.
If you wipe tools with light oil after use, it helps to prevent condensation and subsequent corrosion. Guns and tools were traditionally given (and probably still are) a coating of oil after manufacture and before packing to protect them from dampness and rust.
