My first shooter was made from a BL sapling. No ring chasing.
I just finished a BL bow that has 1 layer of sapwood because it wasn't wide enough for all heartwood.
You may be reading about it in good time in Primitive Archer.
BL is best with a heartwood back.
If I do not have enough heartwood I leave as much sapwood as I think I would need.
Remember that sapwood changes to heartwood as the tree ages.
I posted a shot of the bow on here a month ago.
Here's a similar photo as well as some info.
http://traditionalarchery101.com/Jawge