In the real world I don't think they had contrails. Back in they day we had M-110 8" guns shooting overhead, sounded awesome as the rounds traveled but no contrails. I know contrails are related to atmospheric conditions though having seen artillery shoots in all kinds of weather, from the heat of the desert to cold, humid conditions I've never seen them.
Maybe we get rid of the contrails on shells and move them to airplanes above 10k or something.