The “W” marked magazines are not original to the 75 but are high quality aftermarket magazines currently manufuactured on the original Winchester equipment.  They are made by Wisner’s although they are currently out of stock – http://www.wisnersinc.com/model/winchester-bolt-action-rimfire/

The original magazines are marked in a variety of ways on the floorplate.  I created a master chart a number of years ago so you can determine which vintage magazine is correct for your rifle.  it is a sticky located here – https://www.rimfirecentral.com/threads/more-winchester-magazine-info.368597/

Regards,