Hi Border, I think you my be correct about the bush - I keep popping upstairs to my ‘reloading room’ then back down to think about it then back up for more measurements. I think I’m driving the other half round the bend.
Anyway, I’m using a 192 bush and the brass is springing back .001” giving me .193” OD and an ID of .1725”; hence the issue with the .172” bullets. I thought my check with the full length die was definitive. However, for thoroughness I checked the expander dimensions in the RCBS die. .1735”, allowing for .001” spring back suggests it’s too large (it’s a new decapping rod as I damaged the last one).
My new theory is the brass is getting thinner at the neck (possibly not just the neck) and is now too thin for the 192 bush. I’ll reduce the diameter of the decapping rod expander to give me .002” of neck tension and try a batch of full length sized brass rather than neck sizing. If that solves the problem I’ll either continue to full length size, with the RCBS die, or get a neck die with expander.
Please chip in and correct me if you think I’m following the wrong course.
Cheers
N