I started doing that on knives back in 1982 when I was a full time knife maker. I took some to a knife show in Canton Ohio and sold out. Until then my knives were not selling that fast. I have been a knife maker for many years but did not, and still do not own a proper belt grinder. Cant afford one, so my blade grind was always a flat grind. I was not able to do a hollow grind. The jeweling made the blades look great. It is a little harder to do on a hollow grind since the end brush does not want to seat flat on the blade. I love the look. It serves the purpose on rifle bolts of keeping oil on the surface of the round bolt. The oil holds on to the almost microscopic swirls. Mack