I wouldn't get brain lock, there is really no substitute for the real thing.

Take a good solid rest, relax, good sight picture, control your breathing and squeeze the trigger. Once you get to the point where you can shoot a decent three shot group, give it a try at extended range and even different angles/elevations. Good form has a lot more to do with good shooting than trying to overthink it. And remember it has little to do with how many bullets you fire, much more to do with how accurately you fire every bullet. Consistency is the key.

Try it at different ranges and even from a high seat. A flat shooter like the .243 and "aim off" really doesn't figure in much until you get out to extended ranges.

Any of the top brands of ammo/bullet are going to get the job done. Shot placement is a lot more important than finding the perfect bullet IMO.