From time to time I see people mention that the J-Head nozzle extrudes slightly under what is expected. This may be because I have been drilling out the nozzle orifice with a similar concept to what is done with machine tools. A quality lathe will be built with the tailstock that is about 0.001" high. This way, as it wears, it will eventually line up perfectly before wearing to a point under the center line. Taking this concept to the hot-end, the J-Head nozzle orifice is drilled out slightly smaller than the specification in order to provide room for wear.
A 0.50mm nozzle is therefore drilled out with a 0.4572mm drill bit.
This concept has been creating issues. For example, in Slic3r, the nozzle diameter needs to be set to a lower size in order to generate the proper gcode.
At this point, I am considering abandoning strategy of providing room for wear, and using exact size drill bits. While there will be less room for wear, this should result in a hot-end that is easier to use.