Why do you think the Winchester components made a difference?
Winchester is nothing more than a marketing company, which means it's run by accountants. They buy whatever they can and arrange to have the "Winchester" logo placed on it. (This is why W231 costs more than HP-38.) So when it comes to brass, you had better believe that they are scouring the world to contract with the cheapest maker. And although their primers are only made by Olin, they are probably pushing them cut every corner in order to save a nickel on every 50,000 pieces.
So while I have tons of "Win" brass, it covers 2 decades and possibly 4 to 5 contracts. So there could be huge variations in internal volume, even within a lot of 10 individual pieces.
So I've simply stopped using anything Winchester for testing. It's good enough for competition, but in a test where you want to see low SD numbers to confirm your process, I'm simply not convinced their particular variations are small enough considering the time (hours) it takes to build a set of test cartridges. In other words, the risk is too high considering the immense labor content.