I have been wrong before, but I thought newer Winchesters used a pressure point at the muzzle end of the stock instead of free floating.

I have a good guess you have copper fouled if you are not using a good copper dissolving cleaner. I use Coppermelt, but there are several others on the market. New barrels are rough, and when a bullet goes down the barrel these rough spots pick up copper and other cruds.

What brands of cleaners are you using?

I shoot a lot, 4 hours of 300WSM off of my shoulder would be too rough on me.Is it possible that and 89deg temps could wear on you?