Hey Mulegunner,,welcome from the lurking mode,, I've got right around 170 rounds through my 243 ultra,,,a few different brands. Most anything shoots decent groups.....but the Hornady 75 gr hp and the Cabelas bulk 75 gr vmax group best,,although they group a few inches apart from one another. Hornady high,,,Cabelas low....still decent groups.
I just got some Win. 100 gr powerpoints because as you and I have read this gun supposedly keyholes 100 gr.......mine shot them without any keyhole at 120 yards,,,about a 3 inch group for 3 shots.
Also my Handis' shoot (group) better after several shots,,,first "clean" shot is always 2/3 inches high.
Hope this helps.