I am playing with a Beeman R1, or HW80 for you guys across the ocean. Vintage about 2000 or so. The transfer port was drilled rough as a corncob to my eye with a magnifying glass. Size was perhaps 2.9mm. I drilled it to about 3.1 and still very rough looking ridges. I have read where .125 is optimal in FAC 80s. I did drill again, and got about 80% of the port looking smooth with that pass.
So, the question was wether or not a very roughly machined transfer port is a problem. I also have a leaky cylinder I do believe.