I have tried the plum brown from birchwood casey and it works. I used it on a renegade kit i bought from my friend. I did a small portion of the barrel and decided i liked the look of the in the white metal instead, so I stripped it back off. It was hard to get the process to stop but It finally did after sanding, polishing, and oiling it twice. It seems to work better than most cold blues I have seen. I know it sounds gross, but I have also heard someone say that using your own urine will put a good brown finish on your barrel. I guess the acid in it puts a rust brown on it. This is one of the weirdest I have heard of but it wouldnt cost you anything.