Nylgut String Question

I have Nylgut strings on the Gatcomb banjo that I have posted about and im working on getting the fingering down. The strings sound ok when I picked them but as soon as I try to fret one of them they sound dull and muted. Am I not picking these hard enough or could it be a head tightening issue? It seems like I have to hit the string really hard to sound half decent.

BTW they are in tune.