I bought the forster coax concentricity tool a bit ago and found that I would get more runout on my fired and unsized brass than I should. My gun is a Tikka, so the chamber should be nicely concentric. I would sometimes measure around 0.001" runout on the case neck after firing.
With the way this tool works, the case is supported by a v block on one end that has a stop pin on a spring that keeps the case head in a certain spot on the v block. This means you're rotating the case on it's rim on the v block. Well, if the case rim isn't 100% smooth or circular, that's going to screw up measurements.
I removed the stop pin so that I could spin my case with the web area sitting on the v block rather than the case rim. VOILA! All my fired cases show less than 0.0005" runout on the neck now.
I just thought I'd share in case anyone thought they were getting less than optimal function from their Forster tool or getting more runout than they should on their cases and/or cartridges.
With the way this tool works, the case is supported by a v block on one end that has a stop pin on a spring that keeps the case head in a certain spot on the v block. This means you're rotating the case on it's rim on the v block. Well, if the case rim isn't 100% smooth or circular, that's going to screw up measurements.
I removed the stop pin so that I could spin my case with the web area sitting on the v block rather than the case rim. VOILA! All my fired cases show less than 0.0005" runout on the neck now.
I just thought I'd share in case anyone thought they were getting less than optimal function from their Forster tool or getting more runout than they should on their cases and/or cartridges.
