I've done this on the last two rifles, learned the technique via posts on this forum.
1. Brown the metal just as you usually do.
2. Use Naval Jelly and a maroon Scotch pad to remove the browning, its work. In some accounts I read folks boiled blue after browning, I tested doing the extra step and found it did nothing special, browning is fine. In fact, now that I think on it, the Naval Jelly turns it black anyway, but you rub that off during the process.
3. Blue the metal with your choice of cold blue, really put'er to it.
4. Remove that with the jelly and pad.
you get: French Gray. With all the browning and bluing the finish turns out quite even and I've have a French grayed rifle sitting in the shop this whole last summer (Georgia heat and humidity) and its not even thought of rusting. Its a good finish. It is also work.
dave
PS: If you want more texture on the metal brown it normally, per instructions, but don't card it and keep at it for a week or so. Best to test this one as it depends on current conditions in your shop.