That's a pretty good rule that I try to follow when shooting at the range....but it's also temp. susceptible...i.e. ....hotter days in the summer require a lot longer waiting period than days in the winter. I personally shoot 5-shot groups when working up loads, and let the barrel cool to a reasonable temp. between shots. Some others will shoot a group as fast as they can, feeling the barrel will not heat up that rapidly if the group is shot rapidly. I personally don't subscribe to it. In any regard, if you can't hold your hand on it, let it cool.