I've not made a self hickory, or hickory bellied elb, but I've seen quite a few. The self bow's I've seen seem to have a bit of string follow and they are not popular here in the UK where laminated bows are preferred. The hickory bellied bows generally have a central hard wood core and then a hickory strip backing - the ones I've seen have all been at moderate to medium weight - probably not more than 55lbs. Hickory backing strips on elbs are of course commonplace.
Stan