Bullet run out

I have been on this forum almost daily for the past six years and have learned a lot although still need more info about everything. Recently I have been looking into detecting and correcting bullet runout, but being the cheep person I am I did not want to spend too much money on tools. Saw where some members here had built their own concentricity gauge and became inspired.

I built a crude tool (ripped off the design) and started checking some of my reloads. I indexed each cartridge (at the high spot) and grouped them according to readings I got (3°,6°,8° etc...). I was encouraged by the results of my very limited testing at the range today. *My best 3 shot group with my 338-06 was 1/2" @ 100yards, those three bullets measured a 3° run out. If I *introduced a bullet that had a significantly larger number it impacted the target far from the other two. Prior efforts with the same load netted groups in the area of 1.25".*

So now I'm looking at ways to correct run out (how to build a tool). Who has a design they are willing to share?*

Until I have a tool in my hands I guess that I will just continue to index, categorize and shoot.

edit:
oops!
3°=.003
6°=.006
8°=.008