I have used Char bulls on 1st calf heifers for several years. No more problems than I would expect with other breeds. Less in fact for me, because I use him on Char heifers. If I were breeding any number of heifers from other breeds, I would stay within the breed to avoid heterosis factors. On a first calf heifer, predictability is the name of the game. Pick an easy calver within the breed. I have used Char bulls on BWF heifers, and not had problems, but not large numbers of them. For calving ease, a bull that is almost cow headed will get a second glance from me. Variety is what makes the world go round. Two old cowmen were talking, and the first one said "If everyone had the same opinion, everyone would want to marry my wife." The second one dissagreed say that no one would want to marry her!