Funny i have a Win70 SS Classic same cal, it will shoot way better than I, behind the house we have a 200yd target it will shoot 3 shot groups 1.5 inch or better, me being the weak link.
everyone gave you good advice. Mine doesnt have a break, but a 26 inch tube.
*Check your scope bases & rings (use decent quality mounting HW)
*Check your action Torque (35 inch lbs) correct me if i wrong am someone.
*Take the center trigger guard screw out & shoot a few groups w/o it
*Check your barrel bedding: a quick test is to take a couple small pieces of tape lay the slices neatly in barrel bed at the end of stock (not on any caps) add some upward pressure (torque 2 action bolts & shoot a few groups)
Sometimes trying pin point an issue can be a long process, i full length glassed my rifles, i see others suggesting floating (hornets nest)
I replaced the toothbrush stock with a Bell & Carlson, the 2 piece floorplate with a Williams 1 pc, Rifle Basix trigger, Leupold QR bases / rings topped with a 30mm tubed Leupold scope.
I never knew Winchester to offer a muzzle break & it sounds as though its part of the barrel which leads me to think that has been done outside the factory.
Cutting the barrel back will drop MV
Good luck