Butternut(White Walnut) is the first cousin of Black Walnut. Not known as a bow wood so good for you for prooving that wrong.
One thing I've learned from the Traditional Bowyer's Bible books is that the authors liked to experiment with woods that are not considered 'true' bow woods. Of course, I'm decades behind them, and they've probably already done everything I'm trying, but it's fun to try something new. I never know if the wood is going to work, and if it looks iffy, I can back it. But when I'm done, sometimes I have something that nobody (that I know of) has made before.
My record can attest to this methodology - I've made eleven bows so far. Three made it to being finished bows. One was an experiment, and broke on purpose. The other seven broke in my hands or on the tillering tree. It's disappointing, but I've learned an awful lot. I can almost feel when some woods are reaching their peak now. Of course, most of them just snap and blow up in my face with no warning. I figure that the more I fail, the more I'll know how NOT to fail.
