The first place I'd look would be rate of twist. A little research might be in order regarding that, such as is it different with your Browning versus other similarly chambered rifles. As you probably know, different bullet lengths (roughly corresponding to weight) and bullets driven to different velocities affect accuracy depending on rate of twist of a barrel.

Were the Winchester loads much different than the Fusions? Were the weight and velocity similar?

I think those would be the first places I'd start looking to solve the problem. You might also want to try a heavier or lighter bullet weight in the Fusions and see if it makes a difference. There's no precise 100% accurate way to determine what load a gun will like without experimentation unfortunately.