As a regular save scummer, I can tell you that shot success DOES appear to have some predetermined factor in it. I've never been able to figure out the pattern, but I've seen exactly what you're seeing for years. Generally, the way around it is to put some action between the reload and the shot. Tab to the next soldier and have them do something first and then go back to your original shooter; move 1 square over or some such. Any action seems to "break the destiny".