PzKfW5, I have a Model 17-4 and it has the same problem with hard extractions. I notice in the pictures you furnished that you did not ream all the way through the cylinder. Is there a reason for that?
I'm trying to clean my cylinders with a stainless steel cleaning brush and some J-B from Brownells. If that does not work I was going to look into getting a finish reamer. Any information would be appreciated.