My only venture into a custom was a Jarrett 280 Ackley Improved Beanfield Model - with Leupold 2x9 it was a steady 1/2in five shot group up to 400 yards when the 3x9 ran out of range for my eyes. That said, nearly every Remington M700 I ever had was a 1 MOA out of the box. Any rifle I ever acqired that wasn't capable of 1" before tuning found another home to a less picky person. I have re-barrelled four or five, with Wiseman or Krieger barrels and happy with all.
Before I started liquidating my gun collection over last two years (my kids/grandkids are primary bird hunters and each have two of my prize rifes) but the recent 6.5 Creedmore with Nightforce glass and mounts was better than the Jarret at 400+. A really good shooter could compete at 1000 with this one - but I'm too old to try. My pistol tuning started and stopped at 1911's, primarily barrels, bushings and triggers - I started with stock Colt 1911A1, then Gold Cup because the trigger is better - but candidly buying a Wilson or equivalent made more sense. That said (eyes again), I'm not capable of better than 2 1/2-3 in groups anymore with a pistol capable of 1".