That .243 you have would be just fine at those ranges. Maybe try some other ammomaybe it just doesn't like what your putting though it. If you have access to handloads that would be the way to go. Also you might think of cleaning it real good with good solvents and a brush to remove cooper and powder fouling. Chances are your rifle is just fine 7 years isn't that old for a rifle unless you do some serious shooting. I dont know what kind of scope you have on it but a quaility high magnificationscope will help greatly at those ranges. Maybe just change out the scope,good cleaning and try some different ammo.