You have just changed the pressure of the load. So of course its going to change accuracy. But usually winchester and remington are comparable. Its when you got high dollar thick brass like norma or even soft federal where it usually makes a big change and usually a shoot up in velocity. I know for my STW for instance, I have the same load for winchester brass as I do for the remington, and both shoots the exact same velocity range and grouping.

So yea, you got a strange issue.