Knife River works great using a hammerstone or antler. Heat treatment is very tricky with this material and I think makes the rock work worse. I used to knapp with copper tools and found KR difficult to work but since switching to abo, I've realized that abo tools just eat raw rock for dinner!. In my opinion, abo tools are superior to copper for that reason and many others.
Recomendations:
Work Knife River raw
Try using an antler billet or punch but make sure your platforms are smaller and sharper than for copper