For practice - I just go to Home Depot or Lowe's and find the whitest Cedar 1x4 I can. I rip the spindles square and then cut them at about 9 inches. I then cut the hearths at about 20 inches.
Cut a longer convex taper in the top bearing end and a more flat tip on the hearth end.
They are VERY dry and cedar is almost like cheating when you practice.
You wood combo isn't the problem, I would wager, It is your form. I can use a lot of woods that aren't the best - but I have practiced for hours and hours. Locally, for instance, I use Bald Cypress or Mexican Sycamore. They are harder than a perfect wood should be, but can normally bust a coal pretty easily. When I go back to white cedar - it feels almost too easy.
With all of that said - I am talking about very good conditions. The humidity level in Texas is such that unless you have good conditions and at least dry wood - it is not easy at all.
TF