I just finished jeweling my first round bolt. Based on my experience with the last bolt, (Ruger 10/22, flat bolt), I added 2 layers of shrink tubing over the wire brush to hold all of the bristles together. This reduced the actual circle diameter (close to .250") to the brushes listed diameter of .1875".
As this was a round bolt, I could not just index in the "y" direction but needed to actually rotate the bolt. Based on the diameter of the bolt, it actually turned out that if I wanted a hexagonal pattern, if I made the "x" direction distance .1900" center to center, I could rotate the bolt exactly 20deg to have a chord length of .1900". (see blue picture). My setup used a 3 axis mill (manual z axis, which lets me feel the brush pressure) with a rotary table set on its side with a horizontal center of rotation. (I will put of a picture of this on Monday)
Anyhow, I also changed my compound to .25 parts flux, 1 part oil, and 1 part carbide sanding dust from the grinder. I also needed to build a fixture/collet, to hold the bolt.
I am really happy with how it turned out and for $1.29 investment this turned (get it) out ok. The total time in this project was maybe 2 hrs including planning and mill set-up.
One thing I have learned is the different looks you get with the ratio of brush diameter to center/center distance. The Ruger bolt was further apart than the diameter and has a more round swirl look. The .17 bolt is nearly perfect 1/1 ratio and has what I think of as a fish scale look, which makes me take a second look at it each time because it looks blurry, but when you look at it close up, you can see that it is actually so perfect that your eye cant focus on any one detail.
Sorry the pictures aren't better. The glare plays with the camera focus.