I've gotten on few site's and read post about R-17 and problems with temp mostly from 80 to 100 degree.
I like to spend about year or so shooting rifle before I start hunting with it so lets me go thru our winter to summer shooting here in Co. At our range benches are cover so no direct sunlight but I've shot R-17 in 80-90 degree in 280AI and 284 with no problems at the range. couple years ago was slow hunting antelope and ranch had some PD's on it so set up bench and shot few on off for couple hrs with 270WSM was shooting R-17 and temp was in the 70's and no problems. I did keep my ammo in a cooler and watch barrel as to heat.
I've done the same with other powders so didn't do anything new.
Last year I had the 280AI on 4th season elk hunt temp was 15 below no problem with R-17.
I'm sure some may of had their rifles in direct sun and cooked their ammo and had problem with it.