OK..... a different look at "calm days"
I have 650yds out the window of my reloading room. AND, I live in WA, the absolute calmest place on the planet. Weather here takes days to change. When we get a thunderstorm here it gets talked about on the local news stations......but "calm" is a tricky thing. I've been able to shoot whenever I want, rain or shine, day or nite 24/7 and 365 for most of the 45yrs I've been interested in accuracy, had poured-in-place concrete benches on my properties since 1988, spent time on 3 different home ranges and I STILL HAVE NO IDEA whether or not it's calm out there until I shoot it.
With a GOOD gun.
Some days the flag tails hang limp as granddaddy's....braid, and the bullets flang all over the place randomly. Some days it looks switchy on the flags/ribbons/socks but the main air mass is solid, groups are good if careful.
And at 500yds I really don't believe anyone "reads" the conditions like is routinely done in 100-200 so establishing what your rifle's truly capable of can be hard. But I'm solidly with Randy, it better be capable of 1/4moa!
In my experience out shooting rats on Thee Lone Prairee my personal breakover point is about 350yds, below 350 the "30BR" will always win, at 350 it's a tossup and beyond 350yds it's really dependent on the day but for myself I've never been happy shooting the "30BR" beyond 400 unless I have the sun off my rear flank and a good spotter ....... then it's fun to watch vapor trails, turbulence, glints or even sometimes the actual bullets as they dance thru the pool.
And it's easy to see when it's time to give up the inherent accuracy for the increased BC