Shooting every 4-5 mins the culprit was unlikely caused by heat. I would suspect the culprit to your poor groupings, provided your scope didn't crap out on you, is fouling in the bore. Were you swabbing between shots - or swabbing at all? For sighting in as a minimum you should have been swabbing your bore clean every third shot. Most of us in here swab after each shot for consistancy. Even if its only a spit patch.