42 Arsenal here. I've done quite a lot of experimenting with minimizing heat build up. I'm not saying this is the right way, but it is the best rotation i have found. Tracer x3 > Unload > Heat seeker > Tracer x2 > Rail Shot > Rapid shots 2 or 3 times > repeat. Take into account that the refresh unload can proc. if this happens, prioritize unload. also, only use rail shot with 5 target locks. It is very easy to go overboard because you want to use an ability as soon as the CD is up, but if you do your damage will come to a halt real quick if your vent heat is on CD. It's better to keep a steady flow over time than to go balls to the wall and overheat.