Colin,
In my experience RL-15 is the most temp-resistant of the Reloder series, but in my tests Varget, Big Game and TAC are better in most cartridges.
But as I have pointed out now and then, if you're shooting at shorter ranges (and out to 300 would qualify) then the big factor is where the bullets land. If there's no significant difference in point of impact at various temperatures, then you're good to go!
