What AZshooter said, find some old pulled barrels to cut on. Thats exactly what a friend is doing. Hes had his new lathe for several months now and hasn't attempted a blank yet.
Bore scope is a good idea to see what results you are getting. The real ones are too pricy for me so I got one for my phone on amazon. I used Cerosafe casts and cut cross sections of the chamber to confirm finish quality and correlate it to what I was seeing on the scope. Works pretty well once you get the hang of it. Caveat, the ones for phones have about an inch of focal distance so they don't work for seeing sideways in a barrel and the resolution is low but acceptable.
Thanks for everyone's comments and suggestions. I've decided to get a Green Mountain straight blank for this first project. I may cut and chamber it several times.