Hmmm...corrected @ #16, as previously noted.
Couple of points-
all bullets at the end of their terminal trajectory eventually are overcome by air resistance and loose stability and the yaw of repose overcomes the dynamic balance created by rotational forces and they tumble as the fall to the ground. Usually this is just below supersonic velocity but can vary based on ballistic coefficient and other design factors
wind effect at 875 yards is very hard to read, especially over broken mountainous terrain, so judging drift becomes rather artful vice scientific. The best, even with anemometers and smoke/flags at down range locations have a difficult time hitting game sized targets past 600 yds or so ( a 175 grain 762x51 NATO sniper round (M118LR) drifts about 18 inches at 600 yards in a 5mph full value wind, that would nearly triple at 900 yards, assuming the shooter/spotter could asses the effects down to +/- 1mph or so....
Terminal ballistics ( what happens after the bullet hit flesh) is usually manufactured into hunting bullets based on expected range of impact velocity- a 308 isn’t likely designed to kill game at 875 yards , so in effect the projectile likely had no or very little expansion- and rather low velocity to boot= not very effective or ethical , a 300magnum, on the other hand, would have a better bullet ballistically, resulting on more retained velocity and more much more retained energy and a bullet designed for those ranges.
Anyway, he apparently hit his target lethally ( at least they depict it so) and took the animal home-
A good hunter seeks to get as close as possible, then 10 yards closer.....in my opinion.
Regardig 223 at range- other than a few M1a shooters in the Camp Peery National Matches, all is done with the 223, usually using a 69 or 75/77 out to 300, then an 80 VlD at 600- the target has an X ring 6 inches n diameter at 600, and winning shooters post scores with 199or 200s with X counts in the teens- meaning they, using iron M16 style sights, from a 20 inch AR15, can hold most shots in a 6 inch group, leaking shots left and right usually due to the winds....
My personal best is a modest 195-11x at 600 with an AR15 National match service rifle. This is 20 shots loaded singly and pushing an 80 grain Hornady Amax at about 2775 fps, prone, using only a sling for support.
I use a 300 Win Mag and Hornday 200 grain ELDs for long range hunting, and on the range if I call the wind well, I can hit a 12x12 inch steel target about 70% of the time first round cold bore-supported prone, from 400 to 700 yards, past that my hit prob drops quickly with every hundred yards (my range allows 1200 yards) but I limit ( or my geography limits) myself to game shots not past 500 yards- even though top flite shooters make high percentage 1st shot hits out pas 1200-1500 yards with similar rigs.
Regards