Welcome. Number of questions you had there .... Let me try to touch on a few.
Why is your bow breaking nid limb in the upper limb?
- Hard to say without seeing the bow, but almost all bow failures come down to one of two things, or both. Improper/uneven tillering, or a poor/damaged/bad grain piece of wood. Try using a tillering gizmo.
How long shoudl the ERC dry?
- depends on how large a piece it is, obviously.
Whejn using ERC I usually cut the tree, split into staves, dry them for a few months, rough them out, dry for a while longer, then sinew back ... dry for a month or so. In short, a long time. You're probably talking about months or years unless its a roughed out blank, then you're probably talking weeks-few months. Longer is better because then you know its dry.
Also let me be the first to tell you that ERC is a fickle little bitch. Unless the grain is prefectly straight, knot free and the back is pristine, you need to back it (or at leas tyou'd be smart to). Sinew is not the place to try your first successful bow, it's time consuming, troublesome, expensive, and not conducive to living room bowyery. I'd leave that ERC to dry for a year, and in the mean time flesh out your skills on hickory or other cheap hardwood boards (oak, hard maple, ash, etc).