The soleus initiates slow contractions, while the gastroc initiates fast contractions. (Cordo et al., 1982)

The medial and lateral heads of gastroc function differently from one another; the medial head works much harder than the lateral head to eccentrically resist knee extension.

If you want the calves to grow you need to make them do what they're not used to doing.

The guy with really long Achilles tendons, high calves, short muscle bellies, and a higher percentage of slow twitch muscle fibers will have a much more difficult time making his calves into cows than the guy with shorter Achilles tendons, low calves, long muscle bellies, and a higher percentage of fast twitch muscle fibers.

The main issue with traditional calf raises is that you end up rolling more weight toward your pinky toes as you raise your heels.

Walking Calf Raise