I have yet to see a gun get better groups with a hot barrel than one that is cool. If you are testing reloads or really serious about your groups, try to keep everything consistent. The barrel of the gun, the fouling in the barrel, the temp, etc, etc. When really serious about it, I will wait 10 minutes between shots. When hunting, your usually shooting that critical shot from a cold bore. I talk to snipers for MD, tell me they go to the range sometimes every day and shoot one shot from their cold bore to ensure cold bore accuracy.