Homesteader,
Hey, downrange ballistics are always something of a semi-mystery, and I suspect it doesn't matter much with head-shots!
No doubt the Hornady ballistic tables use "standard atmospheric conditions," 59 degrees F. at sea level. I figured the 50+ foot-pounds in my post with a ballistic program at 75 degrees at 4000 feet above sea level--about the conditions we were shooting in when my partner made the 303-yard shot.
Also, Hornady .17 HMR ammo is loaded with Li'l Gun powder (or at least was, when I visited the factory where it's made a while back). Li'l Gun is good stuff but not particularly temperature-resistant. I've chronographed 17-grain ammo on 85-90 degree days, not unusual when shooting small rodents here in Montana, and gotten over 2700 fps. At 110 degrees it might come close to 3000!
