Ive been working on a load for a 1000yd ar15 .223 p-dog gun. 80gr sierra matchking and ramshot tac powder. Shooting 300 yards, Thursday, 75-80 deg F getting 1.65" 5shot group with 23.5gr powder at an av vel of 2736fps. I think I have my load so I load up 5shot groups of 23.3, 23.4, 23.5, 23.6, 23.7 to verify. Friday, Go with friend to new range, still 300yds, 85-90deg F. 23.3gr 2675 av vel .925" group 23.4gr 2700 1.975" 23.5gr 2718 2.80" former good load 23.6gr 2716 1.975" 23.7gr 2715 1.85" The only thing that changed was the benches( both pretty solid wood benches), the temp(higher), Humidity(higher),light wind right to left both days and the second shooting range was more level by 20ft. elevation or so. My plan is to shoot these loads again to see what happens unless the experts here can shed some light on this mystery.