I don't have much shooting experience, but understand & endorse most of the advice & comments above, except for the more vague comments about poor shooting form that don't include specific details regarding the poor form. I just don't know enough to look at him and determine what all is the poor form I guess.
My question is this however, for the average/below average experience shooter (like me) looking to shoot for hunting accuracy, why wouldn't you zero your rifle at 250 yds? I assume this guy's rifle was zeroed at 100, because I thought there was mention of misses due to improper elevation adjustment for targets over 100 yds?
With a 250 yd zero, a quick ballistics calculator on a 300 win mag 195 gr eldm for "accuracy of water jug" shows no need for elevation or wind compensation with 90 deg 5 mph cross winds out to about 325 yds it seems. So, even with somewhat rushed shots under 325 yds, there is nothing to think about, adjust, or screw up.
I am fairly certain that I would really suck with that 300 win mag, especially after a few shots.
But am I wrong that with a 250 yd zero, reasonable winds, a decent scanning range finder, a dialed in reliable ffp scope with known reticle graduations (Jason mentioned above falling back on these as needed), a stable shooting rest, and a soft recoiling lower caliber rifle setup, shouldn't even a relatively inexperienced guy be able to be pretty deadly out to several hundred yards in these conditions?