Having worked for Les Baer for 21 years, I can truthfully say that we used air dremels for an amazing number of jobs, mostly fitting of parts, where removing a lot of metal was required. Fitting beavertails, matching backs of slides, beveling magwells, flaring ejection ports, etc. In each instance we needed to remove a lot of metal in a hurry. When we got close to the desired dimension, the dremel was put down! I never used a dremel for final polishing or fine tuning the shaping of any part. That was done by hand with files, emory paper, the polishing wheel, whatever. Polishing a chamber was done with a dowel, wrapped with very fine emory paper, chucked in a lathe that turned very slowly. Maybe 120 RPM. The barrel was held in one's hand and carefully slipped over the dowel, to polish the chamber area. A smooth finish was all that was needed, not a mirror shine.
Dremels are fine for removing a lot of metal in a hurry, but they are almost useless for much else. They are the best and most surefire way I know of for destroying a barrel's chamber. We re-barreled a lot of guns because someone tried to "polish" their chamber with a dremel.
If cases eject reliably without being horribly scratched, leave the chambers alone.