Now that the stock is sanded to 400 grain to remove some of the loose fibres, we need to start darkening it. There are all kinds of shortcut products, as I like to call them, but I'm not a fan, so let's do it like they did a couple hundred years ago.
First of all, you need to locate some 70% concentration nitric acid, some places it's called "assay acid" as it's used in the assay of precious metals. It's not as easy to get as it used to be since apparently there are terrorist-like things you can do with it in quantity??? I had a buddy (thanks Brewster!) who works with the stuff and he provided me with the right dilute solution (1:4 acid to purified water). You paint it onto the stock (wear protective gloves!) and allow it to mostly dry. In the old days you would use a heat source like an oil lamp or candle to slowly heat the surface of the stock until the acid oxidizes some of the chemicals in maple, but you can take a shortcut here and use a heat gun with a concentrator tip. It's way faster and you are way less likely to accidentally char part of the stock - be especially careful of thin areas!!!!. when it turns color, it does so very abruptly and becomes a mellow yellow-reddish tint like so:
https://www.milsurps.com/images/impo...DSCN2840-1.jpg
https://www.milsurps.com/images/impo...DSCN2841-1.jpg
No, that's not wet, that's the color it becomes DRY. As an added benefit, if you had bits of iron or steel dust in the grain pores that turned into a greyish bunch of stain spots on your stock when you had wet it to raise the grain (it doesn't sand off), the dilute acid chemically eats the stains away 100% leaving only any residual inletting black on the wood. An added bonus, and also why you don't need to worry about any grey water/iron stains. In case anyone cares, those stains are dissolved iron or steel oxides from chemical reactions with wet tannic acid that was in the wood.
Now need to neutralize all that acid so that it doesn't work on the stock for the next decade and doesn't pit your steel parts when you assemble the rifle. Mix a tablespoon of baking soda with warm tap water and paint it onto the stock. Allow to mostly dry and repeat. This will kill as much of the acid as you need to worry about. If we stopped here and oiled hte stock, it would be a nice chestnnut brown, but it would not look period. It need a little more purply-red. More on that later...
Here is a pic of the stock wet with soda water. This is roughly how it would look if oiled today. Really not that bad.
https://www.milsurps.com/images/impo...DSCN2842-1.jpg
There will be a few new grains that will have raised from all this work. Don't worry about it. If you did a decent job removing the worst of it when you wet the grain the first time and re-sanded, what remains will come off when we oil the stock using a fine steel wool buffer pad later on.
More to follow on traditional stock finishing :)