Webradbury... It is a slower process... But the longer you let the reaction proceed, the darker the finish. Personally, though I have used this method a couple of times, it isn't my favorite, and I have never produced an extremely dark finish with it. My favorite method is a bit more exciting. But it requires the parts NOT be on the gun. What I do is I bury them in a bit of black powder, poured out on a cinder block, and light it. It doesn't take much powder, only a little to mostly enclose the surface I want patina on. Once the combustion is complete, I immediately dowse in cold water. This turns the silver very, very dark brown to almost black immediately. Use this method at your own risk, as I will not be responsible for damages you incur. Never do this indoors.
Again, in both methods, I believe it is the sulfur which is the main catalyst for the rapid oxidation, which is why Liver of Sulfur has been used traditionally.
Matt