I have shot at least a dozen factory loadings in my .243, of those, there are 4 that I can think of that group very well...I could hunt with any of these and be very happy...There are 2-3 more that group OK, under 2 inches at 100 yards....The others group 3-4 inches at 100 yards....Now, there is nothing wrong with my gun, it just has it's preferences...
The interesting thing is, I used to shoot CoreLokts, for about 15 years, a few years back I started trying different ammo on deer, last year I had one factory loading that was giving me flyers...I reached in my ammo box and pulled out a box of CoreLokts that I bought in 1987, shot 3 rounds that you could cover with a quarter...The next day, I went out and bought 2 boxes of the same lot number....Guys they shot to the same point of aim as the old ammo...That's pretty good consistency from some cheap factory ammo...
If you have tried 5-6 different brands of ammo and you know your scope is OK and bedding seems OK, I'd say send it back to the factory and let them figure it out....It's dang hard to trouble shoot on this end of the phone line, been there, done that....