I have to agree with comments that I have seen several threads across several forums, "If you can make a small one, you can make a big one."
In this case I am directly referring to is the micro or 1/6th scale bows. Some call them minis, but mini is closer to the kid size bows. I made my first bow close to 17 years ago. But then I didn't try making another one until Summer of 2006. By that point I was a bit nervous about making a mistake on a $45 stick. When I saw a thread on a scale bows, over at Archery-Interchange, that was the answer I needed.
All that to say, if you want to chase growth rings, get yourself a few branches 18" long and proceed as if it were a full size bow; split, season, layout, cut, and scrape. If you want to make a board bow, head over to the local lumber supply and get a few pieces of scrap. Do your layout. Will it be ELB, AFB, yramid, or other? Now that I'm making these bows as well as the full size variety, I hardly throw away anything. You'd be surprised at how small a piece of horn or other material can be used for strike plates, and overlays.
Good luck and let us know how it goes.