Stretching object animation

I am wanting to make a speargun for a game me and my flatmate are making but I am not sure how to animate the rubber stretching and compressing during the fire and reload animations, does any one know how to do this?

so, it’s like a rubber band? that should be no problem, but how convincing does it have to be? the easiest way to accomplish it btw is with armatures. hooks would also work, but I can’t recall if they work in the game engine or not.