In the paper of David Tubb's recommendations with attached reamer print from Manson the base is shown to be .470?FYI.
JGS has never made a reamer for me... Dave Manson has my reamer specs and will freely share them.
I use a .278" neck / .160 freebore/1 1/2 lead -- for DTAC 115's
Base of the case is .4705"
Our 6XC die set is designed to small base and full length resize.