Part of trying to find a load that consistently shoots well is to eliminate variables. One of those variables is barrel temperature. Every gun reacts differently as the barrel heats up. By allowing the barrel to cool to a similar temp after every shot, you are eliminating barrel temp from the equation. As for time to wait between shots? Depends on your gun and outside conditions, is it cool or warm outside, is it windy or calm..........Just try to wait long enough that the barrel has cooled to a point that it is similar to previous shots.