He said it was the bullets in factory 280 ammo at the time was not the right size for the bore, unlike the .303 ammo.

In my own experiments I have found no real difference in accuracy between open sights and a 4x scope at 100 yards. With the same rifle I can shoot the same size groups at 100 yards with open sights and a bead as I can with an aperture sight, and also a 4x scope - with appropriate used targets for each. I have tested this with several rifles, most lately just this week.