My Lyman rifle is not the GPR but the Trade Rifle. It is also a .54 caliber. I load a .530 and a .018 pillow tick patch with very little effort.

There has to be something your missing on your end, or the rifle is defective. What brand of ball are you shooting? And where did you ever find such a thin patch? I am surprised they do not blow out each time you shoot.

The other question is before you shot (as I am sure you did) you cleaned all that packing grease out of the rifle. This is a very interesting topic as for the life of me I can not figure out why that combination your using would not load real easy actually.