higher pressure will only rear its head, if the outside temps get up in the 90 degree range or more..
I've known people who have taken game at much further distances than 300 yds with that combo...
Good optics help of course...
It would be a very rare occasion for me to be shooting in temps that high. The longest shot I ever witnessed on a deer, was my brother shooting my Remington 788 in 243, many years ago. It was at a measured 485 yards. Now, given his shooting ability, I'd say it was mostly luck. But, the 243 will kill a deer at ranges longer than 300 yards, that's a given. I just try to keep my shots at that distance, mainly because that's the distance of my shooting range, and I know where my rifle shoots at that distance.
