I have a Redfield 6400 20x target scope with target turrets. I bought the scope used, and I can’t set the turrets back to zero after setting the scope. The target turrets has a screw on top. I would think that you would pull the knobs off by pulling up, but these want budge.
Before I pry on them and screw-up something I though I would ask and make sure.

Buck,

I have a 24x Tasco with target knobs and I don't think they can be set to zero.

In my case I don't have a zero as such, but a reading for each range. So my "zero" for 300 yards may be something like 1 (on the inside)
4 outside big scale and 2 smaller grads.