I had the same problem with both a Model 19-4 and a Model 27-2. I traced it to a primer seating problem with the old hand-held primer seating tool I was using.

The ram was a little too short, causing primers not to be seated firmly. In other words, as I would seat a primer in the case, the short ram was a little short so that the primer would not go into the primer hole as far as it needed to....it would go in and stop just short of bottoming out.

Thus, upon firing even mild handloads, the gas would leak by between the primer and the case causing the small pok marks or burn holes.

When I replaced the old tool, my problems went away.