Here is a formula that I'm quoting directly from the book "The modern Kentucky Rifle" by R.H. McCrory, Copywright 1968 "The wood is first treated with a mixture of one part nitric acid and four parts water. Your druggest can mix up a couple ounces of 70% assay acid and water for about 24 cents. Just paint it on and let it dry. Then apply heat from a torch or over a gas flame to cause the acid surface to turn a blushing reddish brown. Take note that it is not intedewd to burn the wood. When the surface is heated sufficiently it will abruptly turn color. Be careful not toburn or char thin sharp portions. Next mix up some baking soda, about half a cup of water and a tablespoon of soda and paint the stock with this to neutralize any acid. after it dries, repeat the soda water treatment again. The nitric acid treatment gives a reddish undertone to the finished stock. Actually, if the stock were oiled after the soda water treatment a very nice chestnut brown finish would result. The next step provides the very dark brown which penetrates into the more porous areas and causes the contrast in the final finish. a stain is made by dissolvingabout 1/2 teaspoon of Potassium Permaginate in an ounce or so of water. This chemical can be bought at your local druggist. in crystal form for about 25 cents per ounce, which will make a lot of stain. The stain is a purple colored liquid which dies the wood a dark brown. (It does the same to clothes and skin, and won't wash off) Paint the stock with several coak-ts of the stain, until its almost black, and allow to dry. When dry it will be lighter in color. paint a couple more coats on and allow to dry again, at which time it gives an almost charred look. We now coat the stock with linseed oil and rub it in with steel wool. This a messy operation but keep at and use plenty of linseed, wipingit clean occasionly to observe the progress you are making. After a few strokes the color will begin to lighten. Keep rubbing until the desired color is obtained The finish will lighten some when the linseed dries." This is the third edition of this book, that I used back in 1973 when I built my first rifle, obviously the prices and help of the druggest probably don't apply anymore. As I recall it was messy to do but worth the effort, and the color is very much like the examples you posted. I haven't built a gun in about twenty years and am just getting back into it after retiring from network engineering, and need something to do over the long cold winter that's approaching. We've already had 36 inches of snow to date, and it's 8 below outside, and winter doesn't start until Tuesday. Your sight and project gun are fantastic, and inspiring. Good Luck