@AshInAmsterdam: user @Pier_ made a thread about nominal vs. real gauges:
Real Gauge of Bass Strings - real gauge vs advertised gauge
Maybe in your specific case there were different real gauges involved. I'm not sure it can be generalised to all rounds vs. flats of same official gauge.
What is likely to have more impact as far as real tension (and consequently setup) and perceived stiffness (both tension proper and, perhaps more importantly, rigidity of the string, as perceived by the player) is the fact flats have less gaps, as mentioned above.
Real Gauge of Bass Strings - real gauge vs advertised gauge
Maybe in your specific case there were different real gauges involved. I'm not sure it can be generalised to all rounds vs. flats of same official gauge.
What is likely to have more impact as far as real tension (and consequently setup) and perceived stiffness (both tension proper and, perhaps more importantly, rigidity of the string, as perceived by the player) is the fact flats have less gaps, as mentioned above.
