Here are step by step photos of the staining process with Ferric Nitrate. I don't really understand why some people insist on making their own with nitric acid (aqua fortis) and iron. Purchasing Ferric nitrate is much safer, and cheaper. I've used Ferric Nitrate on various woods many times (Furniture), though this is the first time I use it on a gunstock. I mixed 30 grams with about 2 cups of water. The ferric nitrate is slightly purple salt that turns a clear yellow when dissolved in water
This is the stock before staining
This is the stock after the ferric nitrate has been generously applied, and allowed to dry. A single application is sufficient. Notice how the wood takes on a greenish grey color.
This is the stock after it has been heated with a heat gun.
This is the stock after the first application of boiled linseed oil.
I use some coarse steel wool to highlight some of the carving.