Honest question. Springfield V6 scales with HP, but the HP scaling is 40%. Of course, HP and ATK are different in many ways. HP has a higher base value in general from all sources, attachment, affinity, etc. There are a lot of ATK% sources that already exist that reduce the effectiveness of ATK% on your attachments, such as the gunsmoke buff and ATK buffs themselves. This means that every increase of ATK% from extreme calibration gives less and less an increase in overall damage. HP, however, has very little of this and means that it would make sense that HP% extreme calibration should yield high returns.
Is it worth extreme calibrating for Springfield? You get better returns but a small multiplier.

>>527280302
>Why is she so much cheerful here
She's high