Jim by the time I finished all but one cavity were casting perfect bullets. The problem cavity is having trouble making a sharp base. Not that it didn't but not consistently like the other 3. I'm thinking at this point the sprue plate may need a touch on the stone at the point of the problem cavity.
As you probably know, that's all about venting. Loosening the sprue plate a little will usually fix it, but other methods work too and I don't really like a floppy loose sprue plate. One trick I do to most of my molds for base fillout is to stone a small bevel on the top edge of each block where the faces meet; the idea is the bevel is another vent under the sprue plate, although a little deeper than normal vent lines.
I also like to use a fly cutter with a V shaped tool to cut a series of vent lines in the top of the mold block, same thing Lee does on their six cavity molds lately. That works really well when done right, allowing air to escape under a snug sprue plate easily so bases fill out well.
One old H&G mold I have is really interesting - it has no vent lines at all on the block faces, they are just smooth and flat, and fit closely. The only vent lines are on top of the blocks, under the sprue plate. The interesting part is that it's one of the easiest casting molds I have, but you wouldn't guess it from comparing the venting to a more modern mold.
