O.K.. I broke it! Not at the tips though. I actually got it to start bending really nicely. I went to gonzo on the tillering string. I did not exercise the libs much and tried to draw it too much. It snapped right on the right side of the handle. Man.
I have more buckthorn, but don't think it's ready to split yet, so I'll start tillering one of the ERC bows I've got roughed out.
Plus, I've got a way to get pretty good amounts of deer sinew for free (and hides) as of tonight, so I'll be giving backing a go.
thanks again for your help.