Re: stock texture
Yep, a natural sponge, but chunks of open cell foam will get you a finer texture, FWIW.
I apply wet freshly mixed gray marine tex with a notched spreader that I make out of a plastic bondo spreader, easily cut with a razor blade. 1/16" X 1/16" triangular notches. This gives me a nice even coat of same thickness, and fast, which is priceless when doing a whole stock. The worst thing you can do is fart around and let it start to set up, which will sink you half way through the sponging.
Then I smooth it out with a flat edged bondo spreader, usually the other half cut off from making the notched one. I smooth it out careful not to change the thickness by dragging it around too much. Just enough to flatten the peaks made by the notched spreader.
When that's done I have roughly 1/16" of marine tex in an even coat. Then using the sponge I pull the texture out by settling the sponge into the epoxy and pulling it straight out, repeat randomly until done, and avoiding creating any kind of pattern.
With it being 1/16" thick, and even, the texture comes out nice and uniform. Thinner will give very small tight peaks, and thicker will give huge peaks and deep pockets, neither of which I find very useful.
After it cures I use a half round bastard file, and a worn piece of 80 grit paper on a sanding block to cut the peaks down to the texture I'm after. When doing that keep in mind how much paint you intend to apply as it will fill the pockets some and dull up the texture. Flat paints do better at leaving more texture to the feel than satins or gloss.