Just to reinforce that it's not the caliber:
I have a semi-custom 270 wsm: stock action, custom barrel and trigger. My one three-shot group at 300 yards measured .946". The 100 yard groups are less than 1/2 inch. My developed load is:
IMR 4350 - 61.0 grains
CCIM (250) primer
Barnes TTSX 130 grain bullet
Muzzle velocity: 3250 fps
I also have a stock Tikka in the same caliber that groups sub-half inch at 100 yards shooting a reduced load for varmints:
SR4759 - 30.0 grains (This is a discontinued powder, but I have 9 pounds of it)
Remington 9 1/2 M primer
Barnes TTSX 110 grain bullet
Muzzle velocity: 2480 fps
Good luck