As the number of shots through a barrel go up, the throat gets eroded
However, loaded right "at the lands" or even a few thousands "into" the lands, some guns produce tighter groups. The problem is, it may be very very sensitive, and a few thousandths error can be crucial.
Because of this, many people intentionally load .020" off the lands, where the group may not be as tight, but the sensitivity to seating depth may be much lower.
If you really want accuracy, I think you are going to have to develop some skills at reloading, and I don't mean novice reloading. That's why I would find a benchrest shooter and ask him to coach you.
You will need several tools, none of which are really expensive. Hornady makes a tool to find the depth of the lands. They also sell devices that go on calipers and allow you to find the spot at which your seating will contact the rifling lands. All this stuff might benefit you more than thousands spent on a gun.
There is a fellow -- I think it is Northwood Shoothing Supplies or something similar -- who sells "RemAge" barrel system that allows you to use a barrel nut to mount a barrel on a Remington 700 receiver, and set the headspace without needing a lathe or machinist or gunsmith. I prefer to do my own gunsmithing (I'm cheap). I learn more that way.
My hunting rifles I load differently than my benchrest rifle.
There is more to this, than I think I will be able to learn in one life.
Wish you the best of luck!