I found that Brownells did not have the crowning tool that I wanted in stock, and instead tried out one of the tools made by Pacific Tool and Gauge.
I got an 11 degree cutter that would work on my Winchester 1885 in 270WSM. I shortened the barrel from 28 inches to 24 inches... Handles much more nicely now, and is slightly more accurate.
Click an image to see it full-size.
Use lots of oil, stop to clean out chips often, go slowly. Take your time.
Having said that, the pictures do not show that at one point, I used an electric screwdriver to turn the tool, as a time-saver. It hogged out the metal more quickly, but introduced chatter that I took out by slow and careful cutting by hand, with light pressure. After that, wet-or-dry sandpaper used wet as shown smoothed it out just fine.