yeah, the goldstar has a pretty fat cylinder, I think 28 or 29 mm bore. Mine has also long since gone.

Ref the seating nipple, I did experiment with a transfer port sleave on TX that was left deliberately slightly protruding, such that it woudl seat the pellet ~0.75mm into the bore. It was very consistent, but did cost me a bit of power - I think it was too deep; something like a 0.3mm protrusion would probably be good.