I had a problem with my safety prime dropping the primer into the primer ram. I finally figured out that it was an alignment problem between the two, but not left or right. The whole safety prime dispenser was a little too low. Yes, I did have the spacer under the bracket, but I had to add two washers under the bracket to get proper alignment. So, the one spacer that comes with the press, and two additional washers added to that.
Once I did that, a little tweaking left and right and now it dispenses primers reliably. As for getting the primer to line up with the case, quite often the case vibrates out of place when pulling it down from the resizing die. I have to nudge the case back in place before I try seating the primer.
Also, some headstamps work better than others. S&B 357mag brass do not have a rounded entry into the primer pocket, so those are more difficult to seat the primers. I have been known to take a crimp remover bit to those to get them to work.