I am not sure what you mean by 'true brown' as seen on most antique rifles--the antiques I have seen vary quite a bit in color--a result of a combination of different woods [even different maples stain differently], different original finishes and ages of use [dirt, grease, etc]. Nitric acid, perhaps with some iron disolved in it, is a typical old-time stain. There are several commercial stains out that I am sure some others will comment on. Some use feibings leather dye, but I have found that to fade some in the light.