I've been fooling around refinishing rifle stocks since I blundered over some articles by Jim Carmichael in Outdoor Life. For about that long (since 1982), I've been using TruOil. It's is a very good product. If one desires, it will produce a very high shine. If one desires a satin finish, that can be done with a little rubbing using 0000 steel wool. I doubt that it is waterproof. Few hobbyist finishes would rate as waterproof. However it is about as water resistant as one can expect. It will do at least a decent job of sealing end-grain and surfaces in general. As might be expected, it works very well on handgun grips. Brushed into the checkering, etc. it leaves a hard finish that stands up well to normal wear and tear.
Tung Oil is what USGI rifle stock were finished in at Springfield Armory. The stocks were simply dipped in the Tung Oil and allowed to air dry. Boiled Linseed Oil was supplied for maintenance of the stocks as issued for use. At the start of WWII it became difficult to obtain the Tung nuts from which to process the oil, so the armories switched to using only BLO. Tung oil has given me good results on rifle stocks. Applied in thin coats rubbed in by hand tung oil has produced a beautiful finish that is moderately water resistant. It is not however a finish suitable for hard use or inclement weather. It will doubtless give a good looking finish to handgun grips. I would not think it would do well for heavy use or hard wear.
For rifle stocks or handgun grips that I will be using hard and that may very well be exposed to rain, etc., I prefer Birchwood Casey TruOil. I seal the inside of the rifle stock w/ clear epoxy which is just about perfectly waterproof. I finish the stock w/ TruOil. For wood that will mostly see display, I like Tung Oil.
And... from time to time, when the moon is non-existant and the dog is asleep... I've been known to pull one of my Springfield 1903's from the gun cabinet and give it a rub of Gunny Paste. Ah... wonderful stuff! Just mix equal parts of Turpentine, Bees wax and Boiled Linseed Oil (1/3, 1/3, 1/3) to make it. Then... rub it on and buff with a soft cloth. Oh my... wonderful stuff! Even my wife likes it! Totally useless as a weather resistant finish... but warm and beautiful to behold! Try it. You might just like it!