Re: maintaining focus
That's for you to figure out on your own, and the game is gonna change drastically when you go from 300 to 600 as now you have to work the wind as well.
I can tell you this much though - just like when I used to row a single shell and I had to be able to visualize all elements of the stroke, you have to be able to visualize everything that you are going to do and how you are going to do it correctly. You must be able to do this away from the rifle, with your eyes closed, inside your head. You consciously go over what you are going to do and at the same time repeat to yourself a self talk that instills confidence in your ability to execute what you are about to embark upon. You focus solely on the performance and ignore the outcome. The outcome (score) takes care of itself; it is a by-product of your performance.
Other than the element of time management for the overall string, your focus is on each and every shot. You learn from the last shot - your call for where it should come up on the target based on your execution of the shot, a correction for the wind - those are the only reasons you look at what happened with a shot that has left the barrel. Otherwise your focus is solely on the round in the chamber.
When on the rifle, you must feel confident that you can hold that X all day, then execute that last bit of pressure (not PULL) on the trigger to make the shot go. When you are sitting on that X ring with the crosshairs, body still, confident that your training coupled with a focused performance means you DESERVE a good score at the end of the day, say to yourself "PRESSURE PRESSURE PRESSURE PRESSURE PRESSURE" as you increase the press on the trigger, confident that you can hold that X all day (at least until you run out of oxygen in your blood and must start over).
You must be confident in your ability to set up and execute. You have an unlimited amount of 10s and X's in you. You must believe that. Why? Because with that confidence and belief in yourself you are now free to turn down the bad shots. Have no doubt - you WILL BE presented with bad shots. The only thing in question is whether or not you TAKE the bad shots. There must be no urgency on getting that shot out of the barrel as you have an unlimited number of 10s and Xs in you and your ability to call on your skills to deliver them you have confidence in.
Sure, there are times when you must shoot fast to deal with wind conditions, but even then that does not alter HOW you perform when you are on the rifle executing one of those unlimited number of 10s and X's inside you.
The art of outdoor long range shooting is a unique blend of high situational awareness combined with the ability to block most all of the stimuli out when on the rifle executing the shot. In certain conditions while you are on the rifle in that totally focused confident zone there is still a part of you that is trying to pick up a change in conditions that dictates a no-shoot situation for the wind clicks or hold point on the rifle. For that day in that stage of the match on that range, know what you are trying to pay attention to that is your indicator and nothing else. Maybe it is the sudden silence of other shooters that have stopped shooting. Maybe it is the appearance or the disappearance of a wind flag in your periferral vision. Maybe it is the appearance of the mirage in your scope. Maybe it is the way the wind feels on your face or neck. Maybe the sound of the wind in the trees. For us Service Rifle shooters, light is another factor we are constantly aware of. Clouds going over, angle of the sun to the target, lit target/dark sights, vice versa, any combination of two, thin clouds versus thick. Eventually it will become most all of those things, and you'll develop the ability to be totally focused on the execution yet still able to catch the condition change indicators.
The last part is the true art of long range shooting.