It has to do with supersonic speed versus subsonic. Supersonic speed will deflect the rain, that is what ballistic expert teach us. To really see the effect of rain check the 308 bullet at 800 meter when it nears the end of its efficacy and starts nearing subsonic speed
Total agreement plus the fact that going transonic likely affects all supersonic bullets IF you're shooting far enough. In my opinion/experiences accuracy is only good until you drop to transonic no matter what the weather. For the most part rain doesnt affect my target shooting. On small caliber bullets at close range 200-250 yards, if anything, I seem to shoot a litte high.