Hello, Bob:

If you pack 13 grains of Dacron (density 1,3 grams/cc) inside your case, you are reducing the volume available inside in about .7 cubic centimeters; the bulk of the Dacron is apparently great, but most of it is air. It is very difficult to know the weight and the volume of the "cork wad" used by Sherman Bell, because cork density varies very much; but if I had to bet, it reduced the available space more than your Dacron and weighted much more than your Dacron. According to that, being the same the load, primer, case and bullet, his 22.000 psi should be higher than yours with Dacron.
I don´t know of any article relating dacron and pressure with pressure readings; but if we are not talking about very light tuffs of the material and the possibility of erratic ignition caused by the powder not placed by the primer (that you must consider if you want to stay in one piece), or the effects of the dacron as a "secondary proyectile", I think you must assume that the greater the dacron weight, the less the available case volume, the higher the weight of the ejecta (bullet and dacron weight) and the higher the pressure, being all the other factors the same.

And now, I will take one step to the side and hear the roar of the opinions about fillers!

If you search the "fillers" or "wads" theme in the forum, you will find lots of information.

Bast wishes

Antonio