Given that the smaller the shot, the denser the lead weight, I reasoned that lead powder might offer the greatest density.
And I found that lead powder was indeed available from a golf supply house. Seems they use lead powder to weight golf clubs.
Not available or shippable to California, I was told. So we moved to Ohio. (Well, there were other reasons.)
Handle with care -- but it does fill the nooks and crannies in hopper cars, etc.
Peter Weiglin