Dixie Gunworks sells an antique stock stain that gives a strong red finish and looks good. If I use it again, I will ad some brown to darken it. You can also buy iron oxide from a number of vendors on the web. It won't darken over time without nitric acid, but it's easier to buy. You can add some brown, or even black dye to give it that dark antique look. Good luck with whatever you use.
Regards,
MR