When I first started, I did this as well.
I did not do a set of soft jaws for the CNC machine though.
I just bored a single hole and did one at a time on the hand-crank mill.
A 3/8" endmill running about 2000 RPM is an amazine tool...
It does make a very square case mouth and very consistent trim lengths when I set the quill stop properly and then come down and touch it.
I only did a few hundred rounds for personal consumption.
The Dillon casefeeder and trimmer just rules for VOLUME...
Randall Rausch
www.ar15barrels.com