When you say "rust"...is it pitted at all or just surface rust? Do exaclty as Werminator says and after that try steel wool or very very fine wet sandpaper with oil. I've used WD40 on steel before and although it gets rid of surface rust, anything deep in the steel will require additional steps. If the rust has pitted the blade, you will need to step up the abrasivenesss. You will see as you go along.
Never waste time deciding between two guns....buy both of them.