I have found this thread to be very useful to someone just getting started in refinishing grips.
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Be aware that Formby's Tung Oil contains almost no Tung Oil. There is a huge difference between pure tung oil and tung oil finish. I'm not suggesting you not use the Formby's, just adding clarification.
How shiny you want your finish to be will dictate what you use, how many coats you put on, and how you sand the surface.