Michael,
In my earlier post above, I had mentioned some ideas such as shooting the same range and conditions. I also mentioned the fact that a lot of benchrest shooters have to deal with these problems. Your right, it is one thing to shoot from a bench, and another to go out in the field.
My personal experience has been to find out how accurate I can make a particular rifle shoot. If there is great consistency at the bench at specific ranges with a accurate handload, you know that the rifle is capable of doing what you want it to do, which builds up your confidence in the rifle and your ability to hit targets with it.
The field however, is another matter for sure. I think that someone can advise and help you with problems like mirage, wind and other problems to a certain point. After that, it becomes a matter of practice with that weapon in the field or match. This is what will help you take that shot at 300+ yards at a coyote if you have to, or a balloon, and still be able to make consistent hits.
Just an example: Take a 243 Remington 700 out in the field over the course of a year and shoot at running jacks out to 200-300 yards. You might shoot as much as a thousand rounds in that time or maybe even more.
Then pick up that rifle when deer season comes around. I will guarantee that if you have to take a shot at a deer that you have jumped and is running full out, chances are you are going to pile him up on the first shot. You have been shooting through mirages, wind, and other elements including movement through out the year at different ranges. You are no longer thinking about all the elements, you just go into remote control and take the shot. You have already shot on many days with different conditions and you have already assessed the conditions for the shot you are taking.
Since I've rambled on too long now, I will narrow my thoughts down to 2 things that I think are important.
Know that your rifle is capable of making tough shots by testing it's accuracy at different ranges on a bench or something solid.
Then take it out in the field and do some serious practice with it. If you don't have a lot of time or ammo, try to make the most of what you have.
Jack is right about match shooting, or for any type of shooting for that matter. If you want to be a serious threat to your competition at the range-or the game you are hunting, then you need to do some serious practicing.
JMHO- Mike