Rolf,
For a smooth silky rust blue I prefer to use Pilkington's classic rust blue from Brownell's. It works every time on just about any steel alloy. How much texture you get will depend on the initial polish - worn 400 grit wet and dry is really all one needs, 600 would be ok. - and how aggressively you rust it which will depend on temperature, humidity and time.
If you want a shinier blue-black, then Mark Lee's Express blue is the way to go. I can tell the difference between barrels finished with these two methods at a glance. My results with the Express blue vary from super to terrible. I restored a Rigby rifle for a customer. The action was one alloy, the barrel another, the rear sight base a third and the barrel band a fourth alloy. Plus the scope and trigger guard were something else. All polished identically, degreased identically and done at the same time. The scope and trigger guard came out a perfect bright, blue black. The action had a yellow cast the first attempt and all the alloys had a different color. Took three attempts to get an acceptable finish on the barrel and action. On most modern barrel steels 12L14 or the stuff Ed Rayl uses, you won't have that much trouble.
Carding with a old pair of jeans will not be aggressive enough for either of these products. Degreased 4/0 steel wool will be much better. You need to get all the surplus oxide off the surface between coats to get an even finish.
If you want to make your own formula, Oscar Gaddy's from the Double Gun Journal is as good as any. I would dilute the base product by 50% and use it like Pilkington's with at least a 3 hour rust between coats at a warm and humid temperature followed by boiling and carding.
If I get a chance I'll photograph two barrels side by side tonight, one done with Pilkington's and one with Mark Lee's and post the photo so you can see the difference.
Tom
