All I can say is that touching up a crown isn't brain surgery, especially if you use a soft enough cutting tool such as brass or lead. With these you are just taking the little nicks off a crown, not recutting it.
I have recrowned dozens of barrels with a Brownells hand tool, and generally in the end use a leather washer (homemade) faced with a piece of fine emery cloth, both on the face of the Brownells tool. This does the same thing as the various brass/lead techniques described here. It doesn't affect the angle of the crown at all. Instead it just does the final polishing.
