As I did research on the internet, I discovered that for some bottled butter is a very controversial topic. I know that many of us (me included) bottle foods a certain way because that's the way we were taught by our mothers and grandmothers (and "no one has ever died"). I felt like it was important, though, for you to be aware of some possible dangers and then armed with the facts, you can decide how you'll proceed.
These articles suggest that you are currently better off buying commercially canned butter. I've seen this product at my local grocery store recently. You can also purchase powdered butter in #10 cans at food storage stores. I have actually stored a little bit of both, but haven't tried either product. Let me know if you've tasted commercially canned butter or powdered butter and can comment on the taste!