I usually hit level 30 at 500 kills and then level 31 at 1000 kills. So the time it takes to go from 30-31 would be apporximately 500 kills. My experience in this only applies to assault rifles though, so I don't know how other weapons compare. --- The only real control we have is over ourselves. So let's get over it that we can't and we won't control anything else.