if you have a rifle you need to hit dead on with you need a more powerful rifle.
primarily this is because shot placement cannot be guaranteed under field conditions.
winding the elevation knob of a scope in the field is fraught with danger.
sooner or later the sight will be on a wrong setting when a shot is fired.
ranging animals is often impossible due to time constraints.
with these facts in the formula, taking advantage of point blank range seems to be the best option for zeroing a hunting rifle.
generally speaking, taking the above into account, +/- 3" max point blank range is in most cases a very useful zero.
a ballistic programme will give a height at 100 yds to zero.
for many cartridges this is somewhere between +2 and + 3" at 100, with the likes of 270 win 130 gn being + 2.5"
this will put the 270 dead on at about 250 yds and 3" low at 300, so aim dead on out to 300.
the 30/06 will be a bit less.
the 375 will be about dead on at 200 yds., and aim dead on out to 250.
for further than the point blank range of the cartridge, you can still aim high, but aim on fur, out to any sensible range that is ethical for hunting.
if you have to aim off fur, don't shoot.
allowing for wind deflection is the same.
never aim off fur to allow for the wind.
you can make a long gun soot short this way, but you can't make a short gun shoot long.
solution? use a sensible cartridge for the situation.
varmint rifles are more suited to a +/- 1.5" point blank, as the targets are smaller.
be aware that at ranges closer than about 20 yds using a scope you will go low.
bruce.