hi-precisions were made in my town, lots of guys around here used them back in the 60s and lots of deer were killed with them. The best edge is use a large new file and push the flat, sharpening two sides at the same time. It can help to put the back blade in a bench vice and put two hands on the file for even pressure,, careful with the fingers around the file. Do the same stroke on sand paper to touch it up for the day. On a bunch that were given away when the plant closed down were seconds, or maybe they were all seconds, not sure. I would shoot each one into soft dirt or foam to check flight and then count your strokes when filing, it is easy to take a lot of metal off of them quickly. I can permanently wreck one in two or three seconds on a grinding wheel.