My sister and I have been grinding pinto beans (we have a very old wheat grinder); and it grinds into a very fine flour like wheat. But it works really well when you mix with either white or wheat flour.
We started experimenting to try and make our wheat flour last a little longer. (We make a lot of bread and wheat is so expensive right now) And mixing the bean flour with white/wheat seems to work really well-- I've made a couple things with the beans/white/wheat mix and they turned out well, and even last week, she made some cinnamon rolls that they were reallllllly fluffy.
Though I do have to warn you, if you do want to try it, the flour will smell a little like beans (when I first used it for a pizza crust, I was like "am I making a horrible mistake here??"), but when it cooks, you can't really taste it. It adds a little nut-flavor, but I don't think you can really taste that it's beans.
She roasted them in the oven last time, but I think that was to make it easier to grind. But if have a grinder, you might want to try it.