I can't argue ether way about the rain effecting the bullet path, But living on the coast (Gulf of Mexico) I can assure you that the humidity has an effect on trajectory and flight path having shot at sea level and then at 8,000 feet+ with the same load and rifle that the drop changed. And having shot my fair share of matches, Many times we had to adjust the zero for different humidity, elevation, Temperature and rain, but fortunately
we were able to adjust for these changes so the matches went as planed.
So I would be inclined to think that rain could change the bullet path If not compensated for. The amount of change would depend on many factors, so that would be different for any combination of cartridge and amount of rain fall.
Just My Opinion
J E CUSTOM