I made a real good hackberry bow a few years back. It might still be in my archived posts. I don't know anything about trapping or recurving, but hackberry does need to be a little overbuilt compared to osage. I used a 3-3.5 inch dia. tree, so the back has a decent crown. It only took on about an inch of set, and is only 62" ttt, I believe. 1.5" width is good. Heat treat the crap out of it, or it's worthless in my opinion. My hackberry is among my best shooters. Good luck and post pics of the progress.