Why can't I set my dwell angle properly?

[1972Blaze]

I put in a new set of points (along with rotor, cap, condenser, wires and plugs). I checked them and the gap was correct at .019. Once running I checked with a dwell meter and it reads right at 40 degrees. I tried to adjust the dwell by turning the screw both directions. There was a noticeable change in the idle speed, but there was almost no movement on the dwell meter. It stayed very close to one side or the other of 40 degrees. I did this with two sets of points with the same result. I want to believe it is a bad meter, but it is a pretty basic piece of equipment. Is there anything mechanical I should check before investing in a new meter? This is a new to me distributor. Would wear on the distributor shaft cam cause this?

By the way, I know it will be recommended, but I do not want to change to HEI.

Thanks for any help.