yeah nylon strings, just the nature of the beast.

the 645 is probably as good as cheap nylon gets that can be printed without a heated chamber. Best on the planet is Mymat nylon from spain.

An alternative is to use flexible pla. Tougher than nylon and if printed fairly dense - it's pretty stiff too.

But you will get stringing.
Slicer settings like: not crossing open spaces if possible will help.
But at th end of the day, nylon is known for it's stringing.