Not all "teak oil" is created equal. Many so-called "teak oil" finishes are really polyurethane finishes that are formulated to look and protect like teak oil. Real teak oil is a good water barrier, as noted by the fact that it is used on boat decks and railings, and reapplying the finish only requires light sanding then apply over the old finish. The poly finishes also offer good water protection, but to recoat the wood after it has been coated, you have to strip then reapply.
As far as a gun finish, teak oil looks very nice, but make sure to wax over it as it does soften and stain when it comes in contact with solvents.
