I believe it is the growth of the new horn that pushes the other horn off. Horns are pretty well grown by the beginning of summer. I think bucks will add a negligable amount of growth to finish out during the summer.
Horn growth begins immediately after dropping the sheath and is fully developed with 10-12 weeks. This is not factual info, but it is what I notice here in NM. The end of March the horns are usually fully developed.
