Yeah, I don't know anything about hackberry, but I probably work with 3-4" saplings more than anything. That crown doesn't bother elm, hard maple, ash, plum, serviceberry, hazel, thornapple, apple, white mulberry, or a dozen other woods not coming to mind.
The only thing is that the roundness often won't give you the width you wish you had for "X" wood and "Y" design. So you have to manage expectations about draw weight, esp. if your stave is on the short side. If you are really worried, ditch the handle and get the middle bending. 40 lbs at 27" sounds very reasonable to me.