Re: hornady concentricty tool?
I got one right after they came out. I use Lee dies, and wanted to see how concentric my reloads were, and figured if I got a guage that also corrected for errors that might be nice.
I found that my .223 full length sized reloads were typically within .001 (must have gotten lucky with this die), my neck sized .223 were typically within .003. My .308 reloads were typically within .004 (both neck and full length). So, I've been able to use this tool quite a bit.
It's pretty easy to set up, and it does help correct for concentricity. It takes a little finesse and practice to figure out how much pressure to use on the little screw. I can get my loads to within .001.
Honestly, it's better to correct the source of the problem than just keep tweaking the resulting reloads...but I figure that this tool can both measure how f*cked your reloads are and correct them while you experiment with fixing the source of the problem for about the same amount of money as just a gauge.
So, to wrap up my ramble...I think it was money well spent.