It's mostly (if not all) a matter of hardness of the ways in the receiver and the internal surface polish.

I say so because I have hand polished and then case-hardened a few late war 98s that were rough and had some degree of binding to them, and when I was done they are as glassy and slick as any high grade Mauser sporter I ever felt, including those that come from some of the more prestigious English gun-houses.

The ones that are "slick" are those that were well polished insider the receivers and then carburized.