Ok this may not be the big numbers of major consistency answer you have been looking for, but I can tell you that we had a Tiny Tim out of an average Hard Core heifer this past spring and he is the best little calf that has hit dirt at our place. We have always had higher birthweights in our cattle and this calf came with a very light pull. His legs weren't fully extended upon presentation and as soon as we got him headed in the right direction everything was good to go. We bred that heifer and another cow back to him and are expecting those calves in Feb. I know it is hard to say from one experience, but we like him and I wouldn't be nervous using him on heifers (we have had bigger Angus calves out of our heifers).