Your cartridges may be correct factory loads. I have a few boxes of the same Winchester ammo. One full but unsealed box holds copper full patch bullets and unplated (copper colored) domed primers. Another Winchester box of the same vintage, but full of old style blanks with paper bullets had flat nickeled primers. The blanks labeling was in red ink to set them apart from the regular ammo label printed in black. Further, it's my understanding that both domed and flat primers coexisted for a while and reloading tools of the era could be had with either cupped or flat primer seating rams.
Re: W marked bullets. I've never seen Winchester bullets marked with a stamped "W" but have observed "W" marked primers.