How do you figure this? How much terminal energy do you believe is necessary to kill a deer?
At 500yds, a 150gn Sierra SBT Game King starting at 2900fps (Sierra's data) will have over 1700fps, and have over 1000ft-lbs of energy. If zeroed at 400yds, then holdover is only 18". Wait for deer to look up, set the horizontal cross-hair on the top of the head, vertical on the shoulder. Result? Dead deer.
Same shot, 165gn Sierra SBT Game King starting at 2700fps is still traveling at over 1700fps and has a terminal energy of almost 1200ft-lbs. Hold over if zeroed at 400yds would be 20". I'd hold pretty much same. Result? Dead deer.
Same shot, 180gn Sierra SBT Game King starting at 2600fps is still traveling at over 1800fps and has 1300ft-lbs of terminal energy. Hold over from 400yd zero is about 20". Same hold.
So, please, tell me how the he!! this chambering is a "non-starter" for hunting deer at distances over 500yds? Each bullet mentioned has sufficient punch and acceptable hold-over. Can Bubba make the shot? Not a chance in he!!. Can someone who shoots and knows his/her rifle? Damn straight!! Just need to make sure that you choose a bullet that will still open up at those lower velocities, hence the Game Kings. Designed to be accurate and perform properly at the lower velocities of long distance.
I'd take the shot, but haven't needed to in many, many years. I can hit a 10" gong at 500yds, 9 out of 10 times with my .308. But that's no off-hand shot, for sure. I'd want to be absolutely sure that the range is right and I would have to be knowing ahead of time that the shot was going to be needed to properly prep for it.