I've seen folks post comments about the use of "cheap diamond files" to extend the life of their flints. I was intrigued and found just such an item online so I placed an order. The set of 6 files was something like $10.00.
They are of varying grit. I picked one of the rougher ones to test on my flints. Over the last few months, when I have been able to focus on my flintlock shooting, I've used that file to dress the rock on my rifle from time to time.
At this time, I am able to report a couple of things that I have learned:
1. Using the file sharpens the leading edge without resulting in loss of length of the flint
nearly as quickly as happens using the traditional knapping method. The distance from the leading edge of the rock to the frizzen face remains constant for a much longer period i.e.: more shots before needing to move the rock forward in the jaws of the cock or replace it altogether. In the first picture (below) you are looking at a flint that has fired a little over 50 shots. It has been touched up along the way with the file. I took this picture after the last 22 shots were fired, after cleaning but before any additional dressing was done. It has not been adjusted forward in the cock since I installed it.
2. Patient use of the file applied evenly across the entire underside of the flint will reduce the natural thickening that occurs when restoring the edge by any method. It also reduces/eliminates the "roughness" or un-evenness of the edge that we see when knapping. As a result, once you acquire a little skill with the file (and use a little patience) your flint will retain a sharp smooth (not jagged) edge that will fully contact the face of the frizzen as it passes across it, even after many shots have been fired. The picture below is the same rock. I tilted the lock a little and put some light underneath it to enhance the area where I am filing away the thickening (note the area that appears to "glow" in the light)
For anyone wishing to give this a try, one lesson I learned was to dress the rock frequently, not wait until it stops working altogether and then try using the file to bring it back to life. I'm not using a lot of pressure on the rock. Just enough to maintain even contact and allow the tool to do the work.
Disclaimer: It's entirely possible that my own knapping skills are not sufficiently well developed and those who have mastered that art will have no problem achieving these same benefits, but that's not me.I'm keeping a couple of these "cheap diamond files" in my shooting box and don't care about any "HC" issues.