I totally agree with you here.I have training and experience as a machinist. I have made a living with the trade over my past 63-years. I find it best to remove sharp corners, unless specified on the print to not break the corner. Chatter is a bugger that is hard to figure out. I noticed that on inside corners to keep the tool moving reduces the propensity for chatter. I learned to cheat and clean up chatter by using things like match sticks or pop sickle sticks covered in emery cloth, rolled emery cloth, rubber infused with abrasive, and scotchbrite.
Accuracy to tenths of a thousand of an inch is for the most part is correct for the atmospheric and environmental conditions at the time. I have had my measuring tools verified both in shop conditions or in climate controlled (not necessarily 68 degrees F/ 20 degrees C). I am of the opinion something indicated to within an amount, the runnout is unaffected by environmental factors. In other words, I indicate a shaft within .001" at 75 degrees and the runnout is checked the next day on the inspection table at 68 degrees the runnout will still be .001.
Metal will do some weird stuff when stressed or stress relieved.
In this case, as far as the corners go, this is a Remington fitted barrel and requires the recessed breech face for the bolt. So the outer ring will not have any effect on “shaving brass”. However, the actual chamber was slightly chamfered, however, it is done so with great caution to help prevent gas pressure leaks in the event of a catastrophic malfunction. Those that are familiar with the Remington design will understand how that works. On edges that I know are susceptible to exposure, I do chamfer the corners.
As far as runout and indicating, I sometimes drive myself insane trying to get it “perfect” and probably shouldn’t. I want to hold myself and my equipment to exceptionally high standards, but I also know that I need to know when I’ve reached my limit. I guess over time I’ll relax a bit!