Rick,
Bagged feed or bulk? Fines are usually not primarily corn, so changing to coarser corn would probably not make much difference. There are two ways to try and eliminate fines without significant changes to your mix: vegetable oil and liquid molasses. We decrease our liquid molasses in the winter to keep the feed from freezing into clumps so much, and increase it in the summer because the moisture evaporates more, making the feed seem drier in the trough. I don't know your mix, but I would increase molasses or oil in your mix by small increments to make the fines stick to the coarse ingredients. (I think the difference in our cold weather mix vs. warm weather mix is 20 pounds of molasses per ton, but I wouldn't experiment with more than 10 pounds at a time.)