Shiester
I have tested quite a few different varnishes, including McCloskey's and they all failed badly, particularly when compared to epoxy. It took over ten coats to build a layer that approached waterproof, but it looked like a coke bottle bottom atop the wood.
I have not seen a product that I have not tested, and constantly look for new ones. None compare to epoxy and superglue, which are the only two that actually seal a stock.
Solvents in finish leave pores when they evaporate. The pores are more than large enough for tiny little water molecules to go through.
One of the reasons spar varnish does well on your drift boat is that it allows the water that gets into the wood through the finish to get back out, once it is back on the trailer and out of the water. It does this very slowly in boat hull terms, but in stock terms it is quite rapid. Very little water is required to warp a stock. This is easy to understand if you look at the ratio of stock surface area to volume.
Oil finishes work ok as a stock finish because they do not seal anything and the water gets through the wood rapidly AND UNIFORMLY. That is why it is a bad idea to seal the barrel channel of an oil-finished stock with something like epoxy or cyanoacrylate which are extremely waterproof. The water getting through the surface finish will cause it to swell toward the barrel. In very dry country it causes the reverse, typically.
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