The steering end of the cast bullet is the "tail" end (the end in the case). The best end of a dbl ended cast bullet is the end OPPOSITE the sprue. Therefore, to gain maximum accuracy, load the ugly end up (the sprue end).
If loading for revolvers, it is also a good idea to have nearly all of the first band out of the case and lightly taper crimp on the tail end of the first band. This helps to align the bullet with the revolver throats.
On the other hand, I load my cast button nosed wadcutters with the sprue down:
The proper answer to the original question is, of course, to shoot your revolver off a rest (preferably with a scope) and make your own determination. The better the quality of the cast bullets, the less importance this makes...
Dale53