Salvo and Molten Blast interaction clarification

The Support Salvo and Dual Wielding a molten Blast gives a wierd result,

on consuming the 3 seals it fires 8 when dual welding and 7 when not.

with scatter shot instead of Salvo the skill fires 6 when Dual wielding and 3 when not.

With both it ires 12 when Dual Wielding and 8 when not