Originally Posted by Timberwolfhd
When I'm working up loads for hunting, I agree, however, you start by saying "once I have settled on a load", what I described is the way to settle on a load.
I use Quickload and Quicktarget computer simulations to help select appropriate loads. The programs do not tell how accurate a given load will be, but they do tell how sensitive the load should be to muzzle velocity variations and to wind deflection if the rifle is perfect. It also predicts muzzle velocities, case fills, muzzle pressure, and bore time. It can even predict velocity variations vs such things as bullet weight variation, charge variation, case volume variation and bore friction variation. All of that can help in estimating which loads may be more accurate but there are enough factors which aren't even addressed to prevent it from actually predicting group sizes. It can tell you a group size that a perfect rifle isn't likely to beat.
The uncertainties of wind estimation increase faster than linearly with increased range both because bullets slow down with distance and the wind is less likely to be the same as at the firing position. At long enough ranges the firing position isn't even the place most sensitive to wind. Vertical stringing resulting from velocity variations increases with more than the square of the distance. It is exactly proportional to the square of the time of flight, but bullets slow down with distance. It helps to have an idea of what group sizes are realistic to achieve before beating yourself to death trying to find find constantly small groups which the range conditions simply won't allow.
Use a good chronograph and wind flags or meters when trying to find good loads. Do most of the testing at the actual distances you expect to shoot. You won't sort out what errors are caused by the rifle, the ammo, and the atmosphere without that. Maybe not with them either but you'll have a better chance.